Apparatus with a wire bond and method of forming the same

ABSTRACT

In some embodiments, a printed circuit board (PCB) comprises a substrate comprising an insulating material. The PCB further comprises a plurality of conductive tracks attached to at least one surface of the substrate. The PCB further comprises a multi-layer coating deposited on the at least one surface of the substrate. The multi-layer coating (i) covers at least a portion of the plurality of conductive tracks and (ii) comprises at least one layer formed of a halo-hydrocarbon polymer. The PCB further comprises at least one electrical component connected by a solder joint to at least one conductive track, wherein the solder joint is soldered through the multi-layer coating such that the solder joint abuts the multi-layer coating.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 13/059,602, filed Feb. 17, 2011, entitled“Apparatus with a Multi-Layer Coating and Method of Forming the Same,”which is a U.S. National Stage Application of International ApplicationNo. PCT/GB2009/001966, filed Aug. 11, 2009 entitled “Halo-HydrocarbonPolymer Coating,” which claims priority to United Kingdom ApplicationNo. GB 0815094.8, filed Aug. 18, 2008, entitled “Wire Bonding;” UnitedKingdom Application No. GB 0815095.5, filed Aug. 18, 2008, entitled“Devices;” and United Kingdom Application No. GB 0815096.3 filed Aug.18, 2008, entitled “Printed Circuit Boards.”

TECHNICAL FIELD OF THE INVENTION

This disclosure relates generally to polymer coatings and, morespecifically, to a halo-hydrocarbon polymer coating for electricaldevices.

BACKGROUND OF THE INVENTION

Many electrical devices comprise electrical components that are solderedto printed circuit boards (PCBs). The metal surfaces on the electricalcomponents and PCBs often oxidize or corrode before being solderedtogether. The oxidation or corrosion of the metal surfaces may preventstrong solder joints from being formed or may reduce the lifetime ofsuch joints. As a result, the electrical devices may be defective or maynot function as long as desired.

SUMMARY OF THE INVENTION

In some embodiments, a printed circuit board (PCB) comprises a substratecomprising an insulating material. The PCB further comprises a pluralityof conductive tracks attached to at least one surface of the substrate.The PCB further comprises a coating deposited on the at least onesurface of the substrate. The coating may cover at least a portion ofthe plurality of conductive tracks and may comprise at least onehalo-hydrocarbon polymer. The PCB may further comprise at least oneconductive wire that is connected by a wire bond to at least oneconductive track, wherein the wire bond is formed through the coatingwithout prior removal of the coating such that the wire bond abuts thecoating.

In other embodiments, a PCB comprises a substrate comprising aninsulating material. The PCB further comprises a plurality of conductivetracks attached to at least one surface of the substrate. The PCBfurther comprises a multi-layer coating deposited on the at least onesurface of the substrate. The multi-layer coating (i) covers at least aportion of the plurality of conductive tracks and (ii) comprises atleast one layer formed of a halo-hydrocarbon polymer. The PCB furthercomprises at least one electrical component connected by a solder jointto at least one conductive track, wherein the solder joint is solderedthrough the multi-layer coating such that the solder joint abuts themulti-layer coating.

In yet other embodiments, an apparatus comprises a substrate comprisingan insulating material. The apparatus further comprises a first contactattached to at least one surface of the substrate. The apparatus furthercomprises a coating deposited on at least one surface of the firstcontact. The coating may comprise at least one halo-hydrocarbon polymersuch that the first contact is operable to conduct an electrical signalthrough the coating to a second contact without removal of the coating.

One or more embodiments may comprise a printed circuit board to which asolder connection is to be made. The surface of said printed circuitboard may have a multi-layer coating comprising one or more polymers.The polymers may be selected from halo-hydrocarbon polymers andnon-halo-hydrocarbon polymers. The thickness of the multi-layer coatingmay be from 1 nm to 10 μm.

One or more embodiments may comprise a printed circuit board to which asolder connection is to be made. The surface of said printed circuitboard may have a multi-layer coating comprising one or more polymers.According to certain embodiments, there may be no solder; or essentiallyno solder, between said coating and conductive tracks of said printedcircuit board.

One or more embodiments may comprise a printed circuit board to which asolder connection is to be made. The surface of said printed circuitboard may have a multi-layer coating comprising one or more polymers.The multi-layer coating may comprise one or more layers of discretepolymers.

One or more embodiments may comprise a printed circuit board to which asolder connection is to be made. The surface of said printed circuitboard may have a multi-layer coating comprising one or more polymers.The multi-layer coating may comprise graded layers of differentpolymers.

One or more embodiments may comprise a printed circuit board to which asolder connection is to be made. The surface of said printed circuitboard may have a multi-layer coating comprising one or more polymers.The multi-layer coating may comprise two or more layers.

One or more embodiments may comprise a printed circuit board to which asolder connection is to be made. The surface of said printed circuitboard may have a multi-layer coating comprising one or more polymers.The first layer, which may be in contact with the surface of the printedcircuit board, may comprise a non-halo-hydrocarbon polymer.

One or more embodiments may comprise a printed circuit board to which asolder connection is to be made. The surface of said printed circuitboard may have a multi-layer coating comprising one or more polymers.

In some embodiments, there may be no, or essentially no, metal halidelayer on the surface of the printed circuit board. In some embodiments,a method of making a connection to a printed circuit board having amulti-layer coating comprises applying solder, and optionally flux, tothe printed circuit board at a temperature and for a time such that thesolder bonds to the metal and the composition is locally dispersedand/or absorbed and/or vaporised. According to certain embodiments oneor more factors are selected such that (a) there is good solder flow,(b) solder covers the substrate (typically a conductive track or pad) onthe printed circuit board, and (c) a strong solder joint is generated.The one or more factors may comprise (a) the substrate characteristics,(b) the coating characteristics, (c) the solder/flux characteristics,(d) the soldering profile (including time and temperature), (d) theprocess to disperse the coating, and (e) the process to control solderflow around the joint.

One or more embodiments may comprise a method of modifying the wettingcharacteristics of a coating comprising one or more halo-hydrocarbonpolymers on a printed circuit board by plasma etching, plasmaactivation, plasma polymerisation and coating, and/or liquid basedchemical etching.

One or more embodiments may comprise a method of modifying the wettingcharacteristics of a multilayer coating by plasma etching, plasmaactivation, plasma polymerisation and coating, and/or liquid basedchemical etching.

In some embodiments, a printed circuit board comprises a substrate andconductive tracks. The surfaces of said printed circuit board may becompletely or substantially encapsulated with either (a) a coating of acomposition comprising one or more halo-hydrocarbon polymers, or (b) amulti-layer coating comprising one or more polymers selected fromhalo-hydrocarbon polymers and non-halo-hydrocarbon polymers, at athickness of 1 nm to 10 μm. According to certain embodiments, thesubstrate comprises a material that absorbs water or solvent basedchemicals. In some embodiments, the substrate comprises epoxy resinbonded glass fabrics, synthetic resin bonded paper, phenolic cottonpaper, cotton paper, epoxy, paper, cardboard, textiles, or natural orsynthetic wood based materials.

In some embodiments, a method of preparing a printed circuit boardcomprises: (a) providing a printed circuit board having anenvironmentally exposed surface, (b) cleaning the surface in a plasmachamber, using gases such as hydrogen, argon or nitrogen, and (c)applying to the surface a thickness of 1 nm to 10 μm of a compositioncomprising a halo-hydrocarbon polymer by plasma deposition, said coatingoptionally following the 3D form of the printed circuit board.

In some embodiments, a method of preparing a printed circuit boardcomprises: (a) providing a printed circuit board having anenvironmentally exposed surface, (b) cleaning the surface in a plasmachamber, using gases such as hydrogen, argon or nitrogen, (c) applyingto the surface a thickness of 1 nm to 10 μm of a multilayer coatingcomprising one or more polymers by plasma deposition. The polymers maybe selected from halo-hydrocarbon polymers and non-halo-hydrocarbonpolymers. The multi-layer coating may optionally follow the 3D form ofthe printed circuit board.

One or more embodiments may comprise using a composition comprising ahalo-hydrocarbon polymer as a flame-retardant coating for printedcircuit boards.

In some embodiments, a method of making a connection between a wire anda substrate may use a wire bonding technique. The wire and/or thesubstrate may be coated with a composition that comprises one or morehalo-hydrocarbon polymers at a thickness of from 1 nm to 2 μm. In someembodiments, the wire bonding technique is ball/wedge bonding. In otherembodiments, the wire bonding technique is wedge/wedge bonding.According to certain embodiments, the wire comprises gold, aluminium,silver, copper, nickel, or iron. In some embodiments, the substratecomprises copper, gold, silver, aluminium, tin, conductive polymers, orconductive inks.

In some embodiments, a method of making a connection between a wire anda substrate may use a wire bonding technique. In some embodiments, onlythe wire is coated with a composition that comprises one or morehalo-hydrocarbon polymers at a thickness of from 1 nm to 2 μm. In otherembodiments, only the substrate is coated with a composition thatcomprises one or more halo-hydrocarbon polymers at a thickness of from 1nm to 2 μm.

In some embodiments, a method of making a connection between a wire anda substrate may use a wire bonding technique. The wire and/or thesubstrate may be coated with a composition that comprises one or morehalo-hydrocarbon polymers at a thickness of from 10 nm to 100 nm.

In some embodiments, a method of making a connection between a wire anda substrate may use a wire bonding technique. The wire and/or thesubstrate may be coated with a composition that comprises one or morehalo-hydrocarbon polymers. In some embodiments, the halo-hydrocarbonpolymer is a fluoro-hydrocarbon.

In some embodiments, a method of making a connection between a wire anda substrate may use a wire bonding technique. The wire and/or thesubstrate may be coated with a composition that comprises one or morehalo-hydrocarbon polymers. In some embodiments, the halo-hydrocarbonpolymer coating remains intact after wire bonding except in the areawhere the connection is made. According to certain embodiments, thehalo-hydrocarbon polymer coating is removed and/or dispersed by theaction of the wire bonding process, without the coating being removed ina separate pre-processing step. In some embodiments, an additionalcoating comprising one or more halo-hydrocarbon polymers is appliedafter formation of the connection.

In some embodiments, a halo-hydrocarbon polymer may be used to preventoxidation and/or corrosion of a wire and/or a substrate prior toformation of a bond between the wire and the substrate by a wire bondingtechnique. According to certain embodiments, a halo-hydrocarbon polymermay be used to allow formation of a connection between a wire and asubstrate under a non-inert atmosphere using a wire bonding technique.

In some embodiments, a device comprises one or more contacts. At leastone of said contacts may be coated with a composition that comprises oneor more halo-hydrocarbon polymers at a thickness of from 1 nm to 2 μm.

In some embodiments, a device comprises an upper contact and a lowercontact. The device may be configured such that the upper contact andlower contact are capable of being brought into electrical contact witheach other. The upper and/or lower contacts may be coated with acomposition that comprises one or more halo-hydrocarbon polymers at athickness of from 1 nm to 2 μm. In some embodiments, the upper and lowercontacts comprise stainless steel, silver, carbon, nickel, gold, tin, oralloys thereof. In some embodiments, the device is a keypad.

In some embodiments, a sensor device comprises one or more sensorelements and each sensor element comprises a contact. The contacts maybe coated with a composition that comprises one or more halo-hydrocarbonpolymers at a thickness of from 1 nm to 2 μm. In some embodiments, theone or more sensor elements are electrodes. In some embodiments, thecontacts comprise carbon, conductive inks, and/or silver loaded epoxy.

In some embodiments, a device comprises one or more contacts. At leastone of said contacts may be coated with a composition that comprises oneor more halo-hydrocarbon polymers at a thickness of from 10 nm to 100nm.

In some embodiments, a device comprises one or more contacts. At leastone of said contacts may be coated with a composition that comprises oneor more halo-hydrocarbon polymers. In some embodiments, the electricalconductivity of the coating in the z-axis is higher than the electricalconductivity in the x-axis and y-axis. In some embodiments, thehalo-hydrocarbon polymer coating provides environmental protection. Insome embodiments, the electrical resistance of the coating can beoptimised for different applications.

In some embodiments, a device comprises one or more contacts. At leastone of said contacts may be coated with a composition that comprises oneor more halo-hydrocarbon polymers. A method for preparing the device maycomprise depositing the halo-hydrocarbon polymer coating by plasmadeposition. In some embodiments, the halo-hydrocarbon polymer is afluoro-hydrocarbon.

In some embodiments, a sensor element comprises a contact. The contactmay be coated with a composition that comprises one or morehalo-hydrocarbon polymers at a thickness of from 1 nm to 2 μm.

One or more embodiments may comprise a method of protecting one or moreupper and lower contacts in a device. The device may be configured suchthat said upper contact and lower contact are capable of being broughtinto electrical contact with each other. The method may comprise coatingthe contacts with a composition that comprises one or morehalo-hydrocarbon polymers at a thickness of from 1 nm to 2 μm. In someembodiments, the coating is applied prior to manufacture of the device.

One or more embodiments may comprise a method of protecting one or morecontacts in a sensor device. The method may comprise coating the contactpads with a composition that comprises one or more halo-hydrocarbonpolymers at a thickness of from 1 nm to 2 μm. In some embodiments, thecoating is applied prior to manufacture of the device. In someembodiments, the deposition technique is plasma deposition.

In some embodiments, a halo-hydrocarbon polymer may be used to coat asurface or surfaces of contacts in a device comprising an upper contactand a lower contact. The device may be configured such that said uppercontact and lower contact are capable of being brought into electricalcontact with each other. In some embodiments, a halo-hydrocarbon polymermay be used to coat a surface or surfaces of a contact in a sensordevice comprising one or more sensor elements.

Applying the coating to a PCB or other device may provide severaladvantages. Various embodiments may have none, some, or all of theseadvantages. One advantage is that the coating may prevent conductivetracks on a PCB from oxidizing. A PCB is often stored for some period oftime before electrical components are soldered to the PCB. If the PCB isuncoated, the conductive tracks on the PCB may oxidize during storage.An oxidation layer on a conductive track may prevent or hinder thesoldering of an electrical component to the conductive track. Byapplying the coating to the PCB prior to storage, a manufacturer mayprevent the conductive tracks on the PCB from oxidizing. By preventingoxidation, the coating may permit the formation of strong solder jointson the PCB.

Another advantage is that the coating may allow an electrical componentto be soldered through the coating without the prior removal of thecoating. The coating may comprise one or more halo-hydrocarbon polymers.In some embodiments, the heat, solder, and/or flux applied during thesoldering process may selectively alter the coating on the particulararea of the PCB where the solder joint is to be formed. In someembodiments, the soldering process may remove the coating only in thearea of the solder joint. Accordingly, once the solder joint is formed,the coating may extend up to (e.g., abut) the solder joint. As a result,a manufacturer may not need to etch or otherwise remove the coatingprior to the soldering process. By eliminating the need for a separateetching or removal step, the coating may make the PCB assembly processsimpler, less expensive, and/or less time-consuming.

Another advantage is that the coating may prevent the corrosion of aPCB. The coating may provide a barrier between a PCB and corrosive gasesand/or liquids. In some embodiments, the coating may prevent liquidsand/or moisture from reaching the substrate and/or conductive tracks ofthe PCB. The coating may prevent the formation of dendrites thatcontribute to short circuits and/or leakage between contacts.

Another advantage is that the coating may exhibit conductivity along anaxis pointing into the plane of a coated surface (the “z-axis”) whileacting as an insulator along the axes parallel to the coated surface.Accordingly, the coating may be applied to a conductive contact withouthindering the ability of such contact to transmit an electrical signalto a mating contact. Thus, in some embodiments, the coating may protectcontacts from oxidation and/or corrosion without hindering theconductivity of the contacts.

Other advantages will be readily apparent to one skilled in the art fromthe description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and forfurther features and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1A-C illustrate a printed circuit board (PCB), according tocertain embodiments;

FIG. 2 illustrates the deposition of a coating on a PCB, according tocertain embodiments;

FIGS. 3A-B illustrate the soldering of an electrical component toconductive tracks of PCB, according to certain embodiments;

FIG. 4 illustrates a PCB comprising a multi-layer coating, according tocertain embodiments;

FIG. 5 illustrates a PCB comprising a multi-layer coating selectivelyapplied to particular regions of the PCB, according to certainembodiments;

FIGS. 6A-B illustrate a keypad comprising contacts that are coated witha coating, according to certain embodiments;

FIG. 7 is a graph illustrating the z-axis conductivity of examplecoatings having various thicknesses, according to certain embodiments;

FIG. 8 illustrates a measuring device comprising a sensor having coatedcontacts, according to certain embodiments;

FIG. 9 illustrates a wire bond that is formed through a coating,according to certain embodiments;

FIG. 10A illustrates a microscope image of ball bonds formed betweenuncoated wires and a coated contact surface, according to certainembodiments;

FIG. 10B illustrates a microscope image of a section view of a ball bondbetween an uncoated wire and a coated contact surface, according tocertain embodiments;

FIG. 11A illustrates a microscope Image of wedge bonds between uncoatedwires and a coated contact surface, according to certain embodiments;

FIG. 11B illustrates a microscope image of a section view of a wedgebond between a coated wire and a coated contact surface; and

FIG. 12 illustrates a PCB having a ball bond and a wedge bond, accordingto certain embodiments.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a printed circuit board (PCB) 10, according tocertain embodiments. PCB 10 may mechanically support and/or electricallyconnect one or more electrical components 12 associated with anelectrical circuit. PCB 10 may comprise a substrate 14, one or moreconductive tracks 16, a coating 18, and one or more electricalcomponents 12.

Substrate 14 in PCB 10 may comprise one or more boards that mechanicallysupport elements of a circuit. For example, conductive tracks 16 and/orelectrical components 12 may be affixed to at least one surface ofsubstrate 14. Substrate 14 may comprise any suitable insulating materialthat prevents substrate 14 from shorting the circuit of PCB 10. In someembodiments, substrate 14 in PCB 10 comprises an epoxy laminatematerial, a synthetic resin bonded paper, an epoxy resin bonded glassfabric (ERBGH), a composite epoxy material (CEM), a phenolic cottonpaper, and/or any other suitable type and/or combination of insulatingmaterial. According to certain embodiments, substrate 14 comprisespaper, cardboard, natural and/or synthetic wood based materials, and/orother suitable textiles. In some embodiments, substrate 14 comprises aflame retardant material such as, for example, Flame Retardant 2 (FR-2)and/or Flame Retardant 4 (FR-4). Substrate 14 in PCB 10 may comprise asingle layer of an insulating material or multiple layers of the same ordifferent insulating materials with or without conductive tracks 16 onany layer.

One or more conductive tracks 16 may be affixed to at least one surfaceof substrate 14. Conductive track 16 is generally operable to conductelectrical signals between two or more components of the circuit of PCB10. Thus, conductive track 16 may function as a signal trace and/or wirefor conducting signals. In some embodiments, conductive tracks 16comprise regions referred to as contact pads. A contact pad ofconductive track 16 may be configured to support and/or connect withelectrical component 12. Conductive track 16 may comprise any suitableconductive material such as, for example, gold, tungsten, copper,silver, aluminium, and/or tin. In some embodiments, conductive track 16may comprise one or more conductive polymers and/or conductive inks.

Conductive track 16 may be formed on substrate 14 of PCB 10 using anysuitable technique. In some embodiments, conductive track 16 may beformed on substrate 14 using a “subtractive” technique. For example, alayer of metal (e.g., copper foil, aluminium foil, etc.) may be bondedto a surface of substrate 14 and then the unwanted portions of the metallayer may be removed, leaving the desired conductive tracks 16. Theunwanted portions of the metal layer may be removed from substrate 14 bychemical etching, photo-etching, milling, and/or any suitable technique.In other embodiments, conductive tracks 16 may be formed on substrate 14using an “additive” technique such as, for example, electroplating,deposition using a reverse mask, and/or any geometrically controlleddeposition process.

In some embodiments, coating 18 may be deposited over one or moreconductive tracks 16 on substrate 14 of PCB 10. Coating 18 may protectconductive tracks 16 from oxidation, corrosion, and/or otherenvironmental hazards (e.g., swelling caused by liquids and/ormoisture). In some embodiments, coating 18 is deposited over conductivetracks 16 on substrate 14 prior to soldering electrical components 12 toconductive tracks 16 of PCB 10. Thus, there may be no solder, oressentially no solder, at an interface 20 between coating 18 andconductive tracks 16 of PCB 10. Coating 18 may permit electricalcomponents 12 to be selectively soldered through coating 18 toconductive tracks 16 without prior removal of coating 18. In addition,or alternatively, coating 18 may permit wires to be wire bonded throughcoating 18 to conductive tracks 16 without prior removal of coating 18.In addition, or alternatively, coating 18 may exhibit low resistanceand/or impedance along the z-axis 22 (i.e., axis pointing into thesurface of PCB 10 to which conductive tracks 16 are affixed) such thatan electrical signal and/or current may be conducted through coating 18between conductive track 16 and electrical component 12 of PCB 10. Inthis context, the term “current” may refer to the flow of electriccharge and the term “signal” may refer to a time-varying and/orspatial-varying electric quantity (e.g., voltage, current, or fieldstrength whose modulation represents coded information). The signal maybe any suitable type of signal such as, for example, a field inducedsignal or a current induced signal.

Coating 18 may comprise any suitable material that protects conductivetracks 16 from oxidation and/or corrosion. In some embodiments, coating18 comprises one or more halo-hydrocarbon polymer materials. The term“polymer” may refer to polymers formed in-situ from single and/ormultiple monomers, linear, branched, grafted, and/or crosslinkedcopolymers, oligomers, multipolymers, multimonomer polymers, polymermixtures, blends and/or alloys of polymers, grafted copolymers, and/orinterpenetrating networks of polymers (IPNs).

The term “halo-hydrocarbon polymer” may refer to polymers with astraight or branched chain or ring carbon structure with zero, one, two,or three halogen atoms bound to each carbon atom in the structure. Thehalogen atoms in the halo-hydrocarbon polymer may be fluorine, chlorine,bromine, and/or iodine. Preferably, the halo-hydrocarbon polymer is afluoro-hydrocarbon polymer, a chiaro-hydrocarbon polymer, or afluoro-chloro-hydrocarbon polymer wherein zero, one, two, or threefluorine or chlorine atoms are bonded to each carbon atom in the chain.In some embodiments, the chain may be conjugated or highly conjugated orhave extended conjugated chains, rings, and/or branches.

The halogen atoms in the halo-hydrocarbon polymer in coating 18 could bethe same halogen atoms (e.g., fluorine) or a mixture of halogen atoms(e.g., fluorine and chlorine). The term “halo-hydrocarbon polymer” asused herein may include polymers that comprise one or more unsaturatedgroups, such as carbon-carbon double and/or triple bonds, and/orpolymers that comprise one or more heteroatoms (atoms which are notcarbon, hydrogen, or a halogen) such as, for example, nitrogen, sulphur,and/or oxygen. Preferably, the halo-hydrocarbon polymer in coating 18comprises less than five percent heteroatoms as a proportion of thetotal number of atoms in the polymer. The halo-hydrocarbon polymer mayhave any suitable molecular weight. The molecular weight of thehalo-hydrocarbon polymer may be selected according to the desiredfunctionality of coating 18. In a preferred embodiment, the molecularweight of the halo-hydrocarbon polymer in coating 18 is greater than 500amu. The halo-hydrocarbon polymer chains in coating 18 may be straightor branched. In some embodiments, there is crosslinking between thepolymer chains in coating 18.

Examples of preferred halo-hydrocarbon polymers include:

-   -   Polytetrafluoroethylene (PTFE), PTFE type material,        fluorinated-hydrocarbons, chlorinated-fluorinated-hydrocarbons,        halogenatedhydrocarbons, and halo-hydrocarbons as well as        copolymers, oligomers, multipolymers, multimonomer polymers,        polymer mixtures, interpenetrating polymer networks (IPNs),        blends, alloys, branched chain polymers, grafted copolymers, and        cross-linked variants of these materials. In a preferred        embodiment, the halo-hydrocarbon polymer In coating 18 is a        polytetrafluoroethylene (PTFE) type material and, in particular,        modified or unmodified polytetrafluoroethylene (PTFE).    -   Polychlorotrifluoroethylene (PCTFE) and copolymers, oligomers,        multipolymers, multimonomer polymers, polymer mixtures,        interpenetrating polymer networks (IPNs), blends, alloys,        branched chain polymers, grafted copolymers, and cross-linked        variants of these materials.    -   Ethylene copolymer of polychlorotrifluoroethylene (EPCTFE) and        copolymers, oligomers, multipolymers, multimonomer polymers,        polymer mixtures, interpenetrating polymer networks (IPNs),        blends, alloys, branched chain polymers, grafted copolymers, and        cross-linked variants of these materials.    -   Copolymer of ethylene and tetrafluoroethylene (ETFE); copolymer        of tetrafluoroethylene and hexafluoropropylene (FEP); copolymer        of tetrafluoroethylene and perfluorovinyl ether (PFA); polymer        of vinylidenefluoride (PYDF); copolymer of tetrafluoroethylene,        hexafluoropropylene and vinylidenefluoride (THY); copolymer of        vinylidene fluoride and hexafluoropropylene (PYDFHFP); copolymer        of tetrafluoroethylene and perfluoromethylvinylether (MFA);        copolymer of ethylene, tetrafluoroethylene and        hexafluoropropylene (EFEP); copolymer of hexyluoropropylene,        tetrafluoroethylene and ethylene (HTE); copolymer of vinylidene        fluoride and chlorotrifluoroethylene; and/or other        fluoroplastics including copolymers, oligomers, multipolymers,        multimonomer polymers, polymer mixtures, interpenetrating        polymer networks (IPNs), blends, alloys, branched chain        polymers, grafted copolymers, and cross-linked variants of these        materials.

Coating 18 on PCB 10 may comprise a single layer or multiple layers ofhalo-hydrocarbon polymers. In some embodiments, coating 18 comprises atleast one layer of halo-hydrocarbon polymers and at least one layer of ametal halide (e.g., metal fluoride) on a conductive surface. Coating 18may have any suitable thickness 24. In some embodiments, thickness 24 ofcoating 18 may be from one nanometers (nm) to ten micrometers (μm). Inother embodiments, thickness 24 of coating 18 may be from one nm to twoμm. In yet other embodiments, thickness 24 of coating 18 may be from onenm to five hundred nm. In yet other embodiments, thickness 24 of coating18 may be from three nm to five hundred nm. In yet other embodiments,thickness 24 of coating 18 may be from ten nm to five hundred nm. In yetother embodiments, thickness 24 of coating 18 may be from ten nm to twohundred and fifty nm. In yet other embodiments, thickness 24 of coating18 may be from ten nm to thirty nm. In yet other embodiments, coating 18is a monolayer of a halo-hydrocarbon polymer (having thickness 24 of afew angstroms (Å)). In a preferred embodiment, thickness 24 of coating18 is from ten nm to one hundred nm in various gradients, with onehundred nm being a preferred thickness 24. In some embodiments, coating18 may be deposited on substrate 14 and conductive tracks 16 such thatan exposed surface of coating 18 is substantially flat (as illustratedin FIG. 1A). In other embodiments, coating 18 may be deposited onsubstrate 14 and conductive tracks 16 such that an exposed surface ofcoating 18 is not flat but instead conforms to a three-dimensionalsurface of substrate 14 and conductive tracks 16 (as illustrated in FIG.1B).

In some embodiments, coating 18 may be deposited on conductive tracks 16and/or substrate 14 as a continuous film. According to certainembodiments, the continuous film may be substantially free of pores suchas, for example, voids, cracks, holes, and/or defects. In someembodiments, the porosity of coating 18 may be configured to provide thedesired permeability of coating 18. For example, altering the porosityof coating 18 may increase or decrease the permeability of coating 18 toliquids, chemicals, gases, and/or solder. The alteration of the porosityof coating 18 may be a physical, chemical, and/or structural change tothe polymer(s) in coating 18. In some embodiments, changing the surfaceenergy of coating 18 may change the permeability of coating 18 toliquids, chemicals, gases, and/or solder. By controlling the relativesurface energy of coating 18 to the surface energy of the penetratingliquid and/or gas, one may increase or decrease the permeability ofcoating 18. Controlling the permeability of coating 18 to water and/orother solvents may be especially desirable for PCBs 10 that aresubjected to liquid environments (e.g., aqueous environments) and/or tosolvents (e.g., during the cleaning process while manufacturing PCB 10).In some embodiments, the porosity of coating 18 may be configured suchthat coating 18 is selectively permeable to particular material(s) butnot to other material(s). For example, coating 18 may be substantiallyimpermeable to water while being permeable to other liquids.

In some embodiments, coating 18 may comprise multiple layers with athin, exposed layer (e.g., upper layer) that is substantially free ofpores. Thus, the exposed layer of coating 18 may be substantiallyimpermeable to gases, moisture, and/or liquids. In such embodiments, theconcealed layer(s) of coating 18 (e.g., the layer(s) between conductivetracks 16 and the exposed layer of coating 18) may comprise pores thatpermit the concealed layer(s) to conduct an electrical current and/orsignal.

According to certain embodiments, coating 18 may exhibit a self-healingproperty. In some embodiments, this self-healing property may be amechanical property that allows coating 18 to move and/or compress inresponse to a physical force and then, once the force subsides, toreturn to its original structure and/or shape. In other embodiments,this self-healing property may permit electrical self-healing of coating18. When a physical and/or electrical force is applied to a particulararea of a coated substrate 14, coating 18 on the particular area ofsubstrate 14 may be compressed and/or otherwise altered. When thephysical and/or electrical force subsides, coating 18 on the particulararea may “heal” and/or otherwise reorganize to cover the particular areaof substrate 14.

Coating 18 may exhibit relatively low gaseous permeability, thusproviding a significant barrier to gaseous permeation and avoidinggaseous corrosion and/or oxidation through coating 18 to conductivetracks 16. In some embodiments, electrical components 12 may beselectively soldered through coating 18 without prior removal of coating18. Solder joints 26 achieved by soldering through coating 18 may bestrong in comparison to solder joints 26 associated with other currentlyavailable surface finishes. In some embodiments, coating 18 may beconfigured to withstand multiple heat cycles. Coating 18 may exhibitchemical resistance to corrosive gases, liquids, and/or salt solutionssuch as, for example, environmental pollutants. In some embodiments,coating 18 may exhibit low surface energy and/or “wettability.” Thematerials in coating 18 and/or the method of depositing coating 18 maybe configured to control the relative wettability of coating 18. Coating18 may be a stable inert material at normal device temperatures (e.g.,at temperature ranges where PCB 10 may be used). Coating 18 may exhibitgood mechanical properties such as, for example, abrasion resistanceand/or adhesion to PCB materials. In some embodiments, coating 18 mayexhibit improved electrostatic protection. Coating 18 may haverelatively low liquid and salt solution permeability, thus avoidingliquid corrosion through coating 18. According to certain embodiment,coating 18 may generally be environmentally beneficial compared toexisting finishes.

Coating 18 on PCB 10 may be continuous, substantially continuous, ornon-continuous over one or more surfaces of PCB 10. In some embodiments,coating 18 is continuous or substantially continuous over surfaces to besoldered and non-soldering surfaces between or adjacent to them.According to certain embodiments, coating 18 is continuous orsubstantially continuous over substantially all exposed and/orvulnerable surfaces of PCB 10. While a substantially continuous coating18 may be preferred to protect PCB 10 from harmful environments, anon-continuous coating 18 may be preferred for other purposes.

In some embodiments, PCB 10 comprises one or more electrical components12 that are affixed through coating 18 to conductive tracks 16 onsubstrate 14. Electrical component 12 may be any suitable circuitelement of PCB 10. For example, electrical component 12 may be aresistor, transistor, diode, amplifier, oscillator, and/or any suitableelement. In some embodiments, electrical component 12 comprises one ormore leads configured to be affixed to a portion of conductive track 16on substrate 14 of PCB 10. Any suitable number and/or combination ofelectrical components 12 may be affixed to PCB 10.

Electrical components 12 may be affixed to conductive tracks 16 onsubstrate 14 using any suitable technique. In some embodiments,electrical component 12 may be connected to conductive track 16 bywelding, laser-enhanced welding, ultrasonic welding, and/or use ofconductive adhesives. According to certain embodiments, electricalcomponent 12 may be soldered through coating 18 to conductive track 16on substrate 14 without the prior removal of coating 18. The solderconnection between electrical component 12 and conductive track 16 maybe referred to as solder joint 26. Prior to the formation of solderjoint 26, coating 18 may protect conductive tracks 16 from oxidationand/or corrosion. In some embodiments, because solder joint 26 may beformed through coating 18 without the prior removal of coating 18,coating 18 may abut solder joint 26. By abutting solder joint 26,coating 18 may protect conductive tracks 16 from oxidation and/orcorrosion even after electrical components 12 are soldered to PCB 10.

Solder joint 26 between electrical component 12 and conductive track 16may be formed using leaded solder or lead-free solder. In someembodiments, soldering through coating 18 does not reduce the strengthof solder joint 26, as might be expected. Indeed, in some embodiments,solder joint 26 formed by soldering through coating 18 may be strongerthan a solder joint on alternative surface finishes. Solder joint 26 maybe formed according to any suitable technique. In some embodiments, aflux (not illustrated) may be used to form solder joint 26. In otherembodiments, a soldering process that uses heat alone (e.g., lasersoldering) could be used to selectively form solder joint 26. In yetother embodiments, solder joint 26 may be formed by wave soldering,which may entail selective fluxing.

As noted above, solder joint 26 may be formed through coating 18 betweenelectrical component 12 and conductive track 16. In this context, thephrase “formed through” may refer to the formation of solder joint 26without the prior removal of coating 18 from conductive track 16. Thus,conductive track 16 may be coated with coating 16 and then, withoutfirst removing coating 18 from conductive track 16, one or moreelectrical components 12 may be soldered to conductive track 16. Thesoldering process may selectively alter coating 18 and may form solderjoint 26 between electrical component 12 and conductive track 16. Thus,the phrase “formed through” may refer to the formation of solder joint26 without the prior removal of coating 18 from conductive track 16.

As noted above, because solder joint 26 may be formed through coating 18without the prior removal of coating 18, solder joint 26 may abutcoating 18. In this context, the term “abutting” may refer to one ormore edges of solder joint 26 directly touching, substantially touching,and/or being in substantial proximity to one or more edges of coating18. Thus, solder joint 26 may border on the portion of coating 18 thatis not selectively altered (e.g., removed) by the soldering process. Insome embodiments, solder joint 26 may abut coating 18 in a singledimension or in multiple dimensions. For example, as illustrated in FIG.1A, solder joint 26 may abut coating in the x-axis and/or y-axisdirection but not in the z-axis direction.

PCB 10 comprising coating 18 may provide advantages over uncoated PCBs10. Coating 18 may provide none, some, or all of the followingadvantages. One advantage is that, in some embodiments, coating 18 mayprotect PCB 10 from oxidizing and/or corroding while being stored. Onceconductive tracks 16 are formed on substrate 14, manufacturers may storePCB 10 for variable periods of time, potentially up to several months oryears, prior to attachment of electrical components 12. If leftuncoated, materials in conductive tracks 16 (e.g., copper) may oxidizein air, resulting in a layer of oxide and/or tarnish forming onconductive tracks 16. Because traditional PCBs 10 lack coating 18,conductive tracks 16 on traditional PCBs 10 may oxidize and/or corrodeduring storage. The longer an uncoated PCB 10 is stored, the moreoxidation may occur. An oxide or corrosion layer on uncoated conductivetracks 16 may hinder the formation of strong solder joints 26. Inparticular, the presence of an oxide or corrosion layer on conductivetracks 16 may result (i) in weak joints with low mechanical strength,(ii) in “dry joints” that have a tendency to fail during operation ofthe device, (iii) in a joint that fails to make electrical contactaltogether, and/or (iv) in the failure of PCB 10 (e.g., failure ordegradation between conductive tracks 16). In contrast, if coating 18 isapplied to PCB 10, coating 18 may prevent oxidation and/or corrosion ofconductive tracks 16 on PCB 10 during long-term storage (e.g., months oryears), thus permitting strong solder joints 26 to be formed onconductive tracks 16 after storage. In embodiments where coating 18 isapplied to metal and/or polymer based electronics, coating 18 comprisinghalo-hydrocarbon polymers may prevent swelling of conductors and/ordevices.

Another advantage is that, in some embodiments, coating 18 comprisinghalo-hydrocarbon polymers may not be as expensive and/or environmentallyharmful as traditional finishes. Manufacturers have applied metalfinishes (e.g., tin, silver, nickel, and/or gold) to areas wheresoldering would be required. The processes for applying these finishesare time consuming, require additional metals to be used, and poseenvironmental problems. These finishes and processes may be expensiveand/or pose health risks. In some cases, manufacturers have usedfinishes comprising organic compounds such as benzimidazoles andparticles of solder-wettable metals or solder. These organic finishes,however, often do not survive multiple heat cycles and exhibit arelatively short storage life before processing. Thus, the traditionalfinishes used by manufacturers are generally expensive, time consuming,and/or require extra steps in the manufacturing process. The traditionalfinishes have also depleted nonrenewable resources such as preciousmetals. In contrast to the traditional finishes, coating 18 comprising ahalo-hydrocarbon polymer may represent a less expensive and/or higherperformance coating 18 that prevents oxidation of conductive tracks 16prior to attaching electrical components 12 by soldering.

Another advantage is that, in some embodiments, coating 18 comprisinghalo-hydrocarbon polymer may prevent the formation of dendrites betweensolder joints 26. Dendrites of metal compounds have been observed toform in gaps between solder joints 26 on uncoated PCBs 10. Dendrites maycause short circuits and electrical leakage between connectors,resulting in failure of PCB 10. In particular, dendrites may form whenmoisture reaches an uncoated substrate 14 and/or conductive track 16 andgenerates metal ions, which are then redistributed by electromigrationin the presence of an electromagnetic field. Dendrites may representmetallic growths that are caused by electromigration and form fern-likepatterns along surfaces. In embodiments where coating 18 is appliedprior to the formation of solder joint 26, coating may not preventliquids from reaching solder joint 26. However, in such embodiments,coating 18 may prevent moisture from reaching substrate 14 and/orconductive tracks 16 of PCB (which is where dendrites may tend to formby ionic dissolution). Thus, coating 18 may protect PCB 10 against theformation of dendrites by (i) preventing moisture from reachingsubstrate 14 and/or conductive tracks 16, and/or (ii) by providing aphysical barrier between conductors on PCB 10. In addition, oralternatively, because dendrite materials may have low adhesion tocoating 18, coating 18 may reduce the formation of dendrites betweenconductive tracks 16 and/or electrical components 12 on PCB 10. Inaddition, or alternatively, coating 18 may prevent electrical shortingbetween conductive tracks 16 due to the presence of ionic species and/ormetals.

Another advantage is that, in some embodiments, coating 18 may protectthe environment from toxic materials in PCB 10. In order to meetstandards for fire safety, PCB 10 may include elements made from flameretardant compounds (e.g., bromine-based compounds such astetrabromobisphenol A (TBBPA)). Such compounds, however, may be toxic,may be difficult to dispose of safely, and/or may pose risks to theenvironment. Applying coating 18 to PCB 10 may protect the environmentfrom such toxic materials. Applying coating 18 may eliminate orsignificantly reduce the need for flame retardant compounds in the basePCB laminate.

FIG. 1A illustrates PCB 10 comprising a single coating layer. In otherembodiments, PCB 10 may comprise multiple coating layers. Although FIG.1A illustrates two electrical components 12 soldered to conductivetracks 16 of PCB 10, it should be understood that PCB 10 may compriseany suitable number and/or combination of electrical components 12.Although FIG. 1A illustrates coating 18 applied to an external surfaceof substrate 14, it should be understood that coating 18 may be appliedone or more internal surfaces of substrate 14 and/or other components ofPCB 10. It should be further understood that coating 18 may be appliedto PCB 10 before and/or after soldering electrical components 12 toconductive tracks 16.

Although FIG. 1A illustrates electrical components 12 soldered toconductive tracks 16, it should be understood that one or moreelectrical components 12 may be affixed to conductive tracks 16 byalternative bonding methods such as, for example, wire bonding. Itshould be further understood that the devices and components illustratedin FIGS. 1-12 are not necessarily drawn to scale.

FIG. 1B illustrates a double-sided PCB 10 that is coated with coating18. The double-sided PCB 10 may comprise one or more layers of substrate14. Conductive tracks 16 may be affixed to opposite sides of substrate14. In some embodiments, conductive tracks 16 on opposite sides ofsubstrate 14 may be communicatively coupled by one or more vias 27. Via27 may comprise a plated hole that provides an electrical connectionbetween conductive tracks 16 affixed to different surfaces and/or layersof PCB 10. Via 27 may be a through-hole via (e.g., via that extendsthrough PCB), a blind via (e.g., via exposed on only one side of PCB), aburied via (e.g., via that connects internal layers of PCB without beingexposed on either surface), and/or any suitable type of via. In someembodiments, coating 18 may be deposited on external and/or internalsurfaces of via 27. For example, coating 18 may line the side wall ofvia 27 that extends through at least a portion of PCB 10. Thus, coating18 may protect vias 27 and internal layers of PCB 10 from corrosionand/or oxidation.

FIG. 1C illustrates electrical component 12 affixed to PCB 10 by awave-soldering process, according to certain embodiments. As explainedabove, PCB 10 may comprise one or more vias 27 through substrate 14.Prior to soldering electrical components 12 to PCB 10, coating 18 may beapplied to substrate 14 such that one or more coating layers coat theside-walls of via 27. After coating 18 is deposited on substrate 14,electrical component 12 may be positioned on a first side of PCB 10 suchthat a lead 29 of electrical component 12 extends through via 27. Thus,an end of lead 29 may protrude through the opening of via 27 on a secondside (e.g., an opposite side) of PCB 10. In some embodiments, solderand/or flux may then be applied around lead 29 of electrical component12 to form solder joint 26. According to certain embodiments, solderand/or flux is applied on the second side of PCB 10 (e.g., around theend of lead 29 protruding through the second side of PCB 10). The solderand/or flux may then flow through via 27 to form solder joint 26 betweenlead 29 and the side-walls of via 27 and/or conductive tracks 16 on asurface of PCB 10. Thus, solder joint 26 may extend entirely orpartially through via 27. The soldering process may alter coating 18along the side-walls of via 27. For example, in conjunction with formingsolder joint 26, the soldering process may remove coating 18 from theside-walls of via 27. Although FIG. 1C illustrates one via 27 in PCB, itshould be understood that PCB may comprise any suitable number of vias27.

FIG. 2 illustrates the deposition of coating 18 on PCB 10, according tocertain embodiments. Coating 18 may be deposited on PCB 10 to protectconductive tracks 16 from oxidation and/or corrosion. In someembodiments, once conductive tracks 16 have been formed on anenvironmentally-exposed surface of substrate 14, coating 18 is depositedover conductive tracks 16 on substrate 14. Thus, coating 18 may bedeposited on conductive tracks 16 prior to soldering any electricalcomponents 12 to conductive tracks 16. Accordingly, coating 18 may be indirect contact with conductive tracks 16 without any solder, oressentially any solder, between coating 18 and conductive tracks 16.Coating 18 may be deposited on conductive tracks 16 according to anysuitable technique. For example, coating 18 may be deposited usingplasma deposition, chemical vapour deposition (CVD), molecular beamepitaxy (MBE), plasma enhanced-chemical vapour deposition (PECVD), highpressure/atmospheric plasma deposition, metallo-organic-chemical vapourdeposition (MO-CVD), and/or laser enhanced-chemical vapour deposition(LE-CVD). In some embodiments, coating 18 may be deposited by a plasmadeposition process that occurs at a low temperature. Such a lowtemperature plasma process may permit coating 18 to be used on manydifferent types of substrates 14. In some embodiments, coating 18 may bedeposited on conductive tracks 16 by the creation of inter-penetratingpolymer networks (IPNs) and/or by surface absorption of monolayers(SAMs) of polymers or monomers to form in-situ polymers and/or polymeralloys. In other embodiments, coating 18 may be deposited using a liquidcoating technique such as, for example, liquid dipping, spray coating,spin coating, sputtering, and/or a sol-gel process.

As illustrated in FIG. 2, coating 18 may be deposited on conductivetracks 16 by plasma deposition. Plasma deposition, which may be used ina wide range of industrial applications, is generally an effectivetechnique for depositing thin film coatings 18. Plasma deposition mayoccur in a reactor 28 that generates a gas plasma comprising ionisedgaseous ions, electrons, atoms, and/or neutral species. Reactor 28 maycomprise a chamber 30, a vacuum system 32, and one or more energysources 34. Reactor 28 may be any suitable type of reactor 28 configuredto generate a gas plasma. Energy source 34 may be any suitable deviceconfigured to convert one or more gases to a gas plasma. For example,energy source 34 may comprise a heater, radio frequency (RF) generator,and/or microwave generator.

In some embodiments, once conductive tracks 16 are formed on substrate14, substrate 14 may be placed in chamber 30 of reactor 28. Vacuumsystem 32 may pump chamber 30 down to pressures in the range of 10⁻³ to10 mbar. Reactor 28 may then introduce one or more gases into chamber30, and energy source 34 may generate and/or direct electromagneticradiation into chamber 30 to generate a stable gas plasma. Reactor 28may then introduce one or more precursor compounds 36 (as gases and/orliquids) into the gas plasma in chamber 30. When introduced into the gasplasma, precursor compounds 36 may be ionized and/or decomposed togenerate a range of active species in the plasma that react (e.g., by apolymerization process) at a surface of PCB 10 to generate a thincoating 18.

Precursor compounds 36 may be selected to provide the desired coatingproperties. In some embodiments, precursor compounds 36 are hydrocarbonmaterials comprising halogen atoms. For example, to form coating 18comprising a halo-hydrocarbon polymer, precursor compounds 36 may beperfluoroalkanes, perfluoroalkenes, perfluoroalkynes, fluoroalkanes,fluoroalkenes, fluoroalkynes, fluorochloroalkanes, fluorochloroalkenes,fluorochloroalkynes, and/or any suitable fluorinated and/or chlorinatedorganic material (e.g., fluorohydrocarbons, fluorocarbons,chlorofluorohydrocarbons, and/or chlorofluorocarbons).

In embodiments where coating 18 is deposited on PCB 10 by plasmadeposition, the nature and composition of coating 18 may depend on oneor more conditions such as, for example, (i) the plasma gas selected;(ii) the particular precursor compound(s) 36 used; (iii) the amount ofprecursor compound(s) 36 (which may be determined by the combination ofthe pressure of precursor compound(s) 36 and the flow rate); (iv) theratio of precursor compound(s) 36; (v) the sequence of precursorcompound(s) 36; (vi) the plasma pressure; (vii) the plasma drivefrequency; (viii) the pulse width timing; (ix) the coating time; (x) theplasma power (including the peak and/or average plasma power); (xi) thechamber electrode arrangement; (xii) the preparation of the incoming PCB10; and/or (xiii) the size and geometry of chamber 30. Plasma depositionmay be used to deposit thin films from a monolayer (usually a fewangstroms (Å)) to ten microns (preferably to five microns), depending onthe above settings and conditions. The foregoing factors may be variedduring the deposition process to build a single-layer, multi-layer,homogenous, and/or non-homogenous coating 18. In some embodiments, theplasma deposition process may only impact the exposed surface (e.g., thesurface affixed to conductive tracks 16) of PCB 10. Thus, the plasmadeposition techniques may be fully compatible with the manufacture ofPCB 10, causing little or no damage or other unwanted effects to PCB 10.In some embodiments, plasma deposition techniques do not expose PCB 10to the relatively high temperatures associated with alternative surfacefinish processes.

In some embodiments, one advantage of plasma deposition may be thatcoating 18 is deposited such that it accesses all surfaces of PCB 10. Asa result, vertical surfaces of PCB 10 (e.g., surfaces only accessiblethrough holes in PCB 10) and/or overhanging structures on PCB 10 may becovered with coating 18. Consequently, coating 18 may protect PCB 10from oxidation and/or corrosion along any sides, edges, points, and/orareas at which conductive tracks 16 contact substrate 14 of PCB 10. Insome embodiments, the plasma deposition process is not limited by thesurface tension constraints that limit the wet chemistry used in othersurface finish processes. Consequently, smaller vias and/or other holesmay be coated.

In some embodiments, reactor 28 may use an active gas plasma to performin-situ cleaning of the exposed surface(s) of PCB 10 prior to plasmadeposition. In such embodiments, prior to introducing precursorcompounds 36 into chamber 30 for the plasma deposition stage, reactor 28may introduce an active gas plasma into the same chamber 30 to cleansubstrate 14 and/or conductive tracks 16 of PCB 10. The active gasplasma may be based on a stable gas such as, for example, a rare gas, ahydrocarbon gas, and/or a halogenated hydrocarbon gas. In someembodiments, the active gas plasma may be based on hydrogen, oxygen,nitrogen, argon, methane, ethane, tetrafluoromethane (CF₄),hexafluoroethane (C₂F₆), tetrachloromethane (CCl₄), other fluorinated orchlorinated hydrocarbons, and/or a mixture thereof. According to certainembodiments, PCB 10 may be cleaned in chamber 30 by the same material tobe deposited on PCB 10. For example, a fluorinated or chlorinatedhydrocarbon such as, for example, tetrafluoromethane (CF₄),hexafluoroethane (C₂F₆), hexafluoropropylene (C₃F₆), and/oroctafluoropropane (C₃F₈) may be used both to clean the surface(s) of PCB10 and to lay down a layer of a halo-hydrocarbon polymer and/or a layerof metal halide (e.g., metal fluoride, metal chloride, etc.) onsubstrate 14.

In some embodiments, where a layer of coating 18 comprising a halogen orhalide-based material is applied directly to conductive track 16 of PCB10, a very thin layer (e.g., five nm or less) of metal halide may formon an exposed surface of conductive track 16. In some embodiments, themetal halide is a metal fluoride such as, for example, copper fluorideor a derivative thereof. The metal halide layer may be robust, may beinert, and/or may prevent the formation on conductive tracks 16 of oxidelayers and/or tarnishes that could prevent effective soldering.

In some circumstances, however, a metal halide layer on PCB 10 may beundesirable if it results, for example, in intermetallics that arevulnerable to weakening under specific environmental conditions. In suchcases, depositing a first coating layer comprising anon-halo-hydrocarbon material (e.g., polythene and/or polypropylene) onPCB 10 may prevent the formation of a metal halide layer when a secondcoating layer comprising a halo-hydrocarbon polymer is deposited.

Although FIG. 2 illustrates a single PCB 10 in chamber 30 in reactor 28,it should be understood that any number of PCBs 10 may be simultaneouslyplaced in chamber 30 and coated with coating 18. Although FIG. 2illustrates the formation of coating 18 on PCB 10 by plasma deposition,it should be understood that coating 18 may be deposited on PCB 10 usingany suitable technique.

As explained above, once coating 18 is deposited over conductive tracks16 on substrate 14, electrical components 12 may be affixed throughcoating 18 to conductive tracks 16. Electrical components 12 may beaffixed to conductive tracks 16 using any suitable technique such as,for example, soldering, wire bonding, electrostatic bonding, and/or Vander Waals bonding. In some embodiments, electrical components 12 may beconnected to conductive tracks 16 by using an adhesive on coating 18(thereby making use of the z-axis conductivity of coating 18).

FIGS. 3A-B illustrate the soldering of electrical component 12 toconductive track 16 of PCB 10, according to certain embodiments. Asillustrated in FIG. 3A, electrical component 12 may be soldered throughcoating 18 without first removing coating 18 from conductive track 16.The soldering process may comprise applying heat and solder 38 to aparticular area of PCB 10 where solder joint 26 is to be formed. Heatmay be applied to solder 38 using any suitable heat source such as, forexample, a soldering iron 40. In some embodiments, the soldering processmay also comprise applying flux 42 to the particular area of PCB 10. Theheat, flux 42, and/or solder 38 may selectively alter coating 18 at theparticular area of PCB 10. In some embodiments, altering coating 18 mayrefer to removing coating 18 from the particular area of PCB 10. Coating18 may be removed by applying solder 38, and optionally flux 42, to PCB10 at a temperature and for a time such that solder 38 bonds toconductive track 16 and coating 18 is locally dispersed, absorbed,vaporised, dissolved, and/or degraded. In some embodiments, alteringcoating 18 may comprise changing the structure, porosity, and/or surfaceenergy of coating 18. For example, fluxing may alter the surface energyof pores in coating 18, which may change the wettability of coating 18such that solder 38 can flow through pores in coating 18 to conductivetrack 16. Thus, in this example, solder joint 26 may form an electricalconnection through coating between electrical component 12 andconductive track 16. As another example, the soldering process mayselectively alter coating 18 by inducing voids (e.g., cracks) and/orcausing voids to propagate in the particular area of coating 18 wheresolder 38 and/or flux 42 is applied. Preferably, one or more factors areconfigured so that the soldering process achieves good solder flow,covers a portion of conductive track 16 on substrate 14 with solder 38,and/or forms a strong solder joint 26. These factors may include: (i)the characteristics of substrate 14, (ii) the characteristics of coating18, (iii) the solder/flux characteristics, (iv) the soldering profile(including time and temperature), (v) the process to disperse coating18, and (vi) the process to control solder flow around solder joint 26.

In some embodiments, the action of flux 42 and temperature alone mayinteract with the halo-hydrocarbon polymers in coating 18 to altercoating 18 locally at the particular area of PCB 10 to which flux 42 isapplied. According to certain embodiments, altering coating 18 at theparticular area of PCB 10 may comprise removing coating 18 from theparticular area of PCB 10. Solder 38 and/or flux 42 may be heated to anysuitable temperature depending at least in part on the composition ofsolder 38. In some embodiments, solder 38 and/or flux 42 are heated tobetween 200° C. and 300° C. According to certain embodiments, solder 38and/or flux 42 are heated to between 240° C. and 280° C. In a preferredembodiment using lead-free solder 38, solder 38 and/or flux 42 areheated to approximately 260° C.

The action of flux 42 and/or temperature may locally disperse, absorb,vaporise, dissolve, and/or degrade coating 18 comprisinghalo-hydrocarbon polymer. Thus, coating 18 may only be altered at (e.g.,removed from) the particular area of PCB 10 where solder 38 and/or flux42 is applied. As illustrated in FIG. 3B, coating 18 may remain attachedto the surface of PCB 10 right up until solder joint 26. By abuttingsolder joint 26, coating 18 may provide environmental protection ofconductive tracks 16 of PCB 10 right up to solder joint 26.

According to certain embodiments, there may be a balance between thetime required to alter coating 18, the temperature required to altercoating 18, and/or the acidity or aggressiveness of flux 42. Thus,milder fluxes 42 may suffice if higher temperatures are used, and viceversa. In some embodiments, a metal halide layer (e.g., copper fluoride)may reside between conductive track 16 and a halo-hydrocarbon layer incoating 18. The metal halide layer may exhibit a self fluxing actionwhen heat is applied to a particular area of PCB 10. The solderingprocess may take advantage of this self fluxing property. In someembodiments, the metal halide layer and/or the decomposition ofhalo-hydrocarbon polymers in coating 18 may release fluorine and/orhydrogen fluoride (HF) to initiate fluxing (self fluxing) during thesoldering process. Due to this self fluxing property, if a sufficientlyhigh temperature is used during the soldering process, solder joint 26may be formed without using any flux 42.

Any suitable solder 38 may be used to form solder joint 26. In someembodiments, solder 38 may be a fusible metal alloy having a meltingpoint in the range of 90° C. to 450° C. In some embodiments, solder 38is a tin/lead solder 38 such as, for example, 60/40 Sn/Pb or 63/37Sn/Pb. In other embodiments, solder 38 is a lead-free solder 38 such as,for example, an alloy comprising tin, copper, silver, bismuth, indium,zinc, and/or antimony. Examples of lead-free solder 38 include SnCu0.7,SnAg3.5Cu0.7, and SnAg3.0Cu0.5. In some embodiments, solder 38 maycomprise a powdered metal that is suspended in flux 42. The mixture ofthe powdered metal and flux 42 may be referred to as a solder paste.

In embodiments using flux 42 to form solder joint 26, any suitable flux42 may be used. In some embodiments, flux 42 may be a mild flux 42 suchas, for example, a “no-clean” flux (e.g., a rosin flux) that does notrequire a subsequent step of cleaning PCB 10. In other embodiments, flux42 may be an organic flux 42 such as, for example, an organic acid(e.g., lactic acid, acrylic acid, etc.), an organic salt (e.g.,dimethylammonium chloride (DMA HCl)), and/or an organic amine (e.g.,urea). In yet other embodiments, flux 42 may be a resin/rosin flux 42such as, for example, a synthetic resin or a natural rosin. In yet otherembodiments, flux 42 may be an inorganic flux 42 such as, for example,an inorganic salt (e.g., zinc chloride, sodium chloride, potassiumchloride, sodium fluoride, etc.) and/or an inorganic acid (e.g.,hydrochloric acid, nitric acid, etc.). In yet other embodiments, flux 42may be a halide free flux, a no-residue flux, and/or a low solids flux.In addition, or alternatively, industrial fluxes 42 may be used, suchas, for example, fluxes 42 used for general soldering, brazing, welding,cleaning, or etching a metal surface. An example of such an industrialflux 42 is borax. The choice of flux 42 may depend on the nature ofcoating 18, especially the particular thickness 24 and composition ofcoating 18. A thicker, more resistive coating 18 may require using amore aggressive flux 42. In addition, or alternatively, the choice offlux 42 may depend on the wetting properties of the materials in coating18. A composition that comprises the active ingredient or ingredients offlux 42 and that selectively alters coating 18 on PCB 10 (e.g.,selectively removes coating 18) may be used in place of flux 42.

As explained above, coating 18 permits the formation of good solderjoints 26 on conductive tracks 16 of PCB 10. One or more factors may becontrolled to achieve good quality, strong solder joints 26 on PCB 10.These factors may include: (i) the wetting characteristics and/orsurface energy of the coated substrate 14 and/or PCB 10; (ii) thesurface roughness of the coated substrate 14 and/or PCB 10; (iii) thesurface roughness of conductive tracks 16 on substrate 14; (iv) thecomposition of solder 38 and/or solder paste (including active agentsand/or solvents); (v) the temperature profile of the soldering process,which may include optimizing profile temperatures and residence times toimprove wetting performance of solder 38, solder paste, and/or activecomponents; (vi) the size and/or geometry of conductive tracks 16 on thecoated substrate 14; and/or (vii) the particle size of componentspresent in solder 38 and/or solder paste. In some embodiments, thestrength and/or quality of solder joint 26 may be enhanced by thepre-treatment, cleanliness, and/or surface preparation of conductivetracks 16 on substrate 14. Conductive tracks 16 may be cleaned by asurface treatment of plasma gas, sulphuric acid, and/or hydrogenperoxide and/or by a persulphate-based etchant process. According tocertain embodiments, the aperture size and/or thicknesses of the solderpaste stencil may be configured to control the quantity, position,wetting, and/or spread of the solder paste dispensed on conductivetracks 16 on the coated substrate 14.

In some embodiments, the quality and/or strength of solder joint 26 maybe enhanced by balancing the viscosity and surface tension of the solderpaste with temperature to (i) control the wetting and flow of the solderpaste on conductive tracks 16 and/or (ii) control the capillary actioncaused by electronic components on conductive tracks 16. This capillaryaction may tend to displace the solder paste from its desired location,especially if Fine Pitch and/or Ball Grid Array (BGA) soldering is used.According to certain embodiments, the quality and/or strength of solderjoint 26 may be enhanced by controlling the composition, chemicalstability, and/or thickness 24 of coating 18 such that the solder pasteselectively alters coating 18 on a particular area on the surface ofsubstrate 14. In some embodiments, the quality and/or strength of solderjoint 26 may be enhanced by controlling the chemical action of theactive component in the solder paste with the halo-hydrocarbon polymersin coating 18 to facilitate the selective alteration (e.g., selectiveremoval) of coating 18. The quantity and/or composition of the activecomponents in the solder paste may be optimised to facilitate thisaction.

Although FIGS. 3A-B illustrate a soldering process that uses solder 38,heat, and flux 42 to form solder joint 26, it should be understood thatsolder joint 26 may be formed through coating 18 using solder 38 andheat without any flux 42. Although FIGS. 3A-B illustrate solder joint 26formed through a single-layer coating 18, it should be understood thatsolder joint 26 may be formed through a multi-layer coating 18.

FIG. 4 illustrates PCB 10 comprising a multi-layer coating 18, accordingto certain embodiments. The term “multi-layer” may refer to coating 18that comprises two or more distinct and/or graded layers 44 of polymers.Where a multilayer coating 18 comprises distinct layers 44, each layer44 may comprise a discrete chemical composition. Where a multi-layercoating 18 comprises graded layers 44, individual layers 44 may form aregion of intermediate composition between the individual layers 44. Thematerial(s) in the region of intermediate composition may have varyingmolecular weight, chemical composition, structure, geometry, porosity,and/or other properties. Thus, multi-layer coating 18 may comprisemultiple distinct layers 44 of polymers and/or may comprise multiplegraded layers 44 of polymers.

In some embodiments, the multi-layer coating 18 may comprise a firstlayer 44 a comprising a first type of polymer and a second layer 44 bcomprising a second type of polymer. In other embodiments, the firstlayer 44 a and second layer 44 b of the multi-layer coating 18 maycomprise polymers that have a similar chemical composition but differentstructures, different degrees of conjugation, and/or different weights.In some embodiments, a particular layer 44 in the multi-layer coating 18may comprise a single type of halo-hydrocarbon polymer. In otherembodiments, a particular layer 44 in the multi-layer coating 18 maycomprise a mixture of different types of halo-hydrocarbon polymers.According to certain embodiments, each layer 44 in the multi-layercoating 18 may comprise the same or different compositions ofpolymer(s). In some embodiments, each layer 44 comprises similarprecursor compounds 36 that are processed differently to form each layer44. This may result in each layer 44 having different polymers,different polymer networks, different molecular weights, differentsizes, different physical structures, and/or differences in otherproperties. In other embodiments, each layer 44 comprises differentprecursor compounds 36, which may cause each layer to comprise differentmaterials and/or material properties.

The multi-layer coating 18 on PCB 10 may comprise any suitable number oflayers 44. In some embodiments, the multi-layer coating 18 comprisesfrom two to five layers 44. In other embodiments, the multi-layercoating 18 comprises from two to four layers 44. In a preferredembodiment, the multi-layer coating 18 comprises two or three layers 44.In embodiments where coating 18 comprises three or more layers 44, themulti-layer coating 18 may be configured such that two or more layers 44that are not adjacent to each other comprise the same polymer. For someapplications, the number of layers 44 in the multi-layer coating 18 maybe selected to enhance the anti-reflective and/or dielectric propertiesof the multi-layer coating 18. In such embodiments, the multi-layercoating 18 may comprise a higher number of layers 44 (e.g., four ormore) with the thickness and/or geometry of each layer 44 beingcontrolled. In such embodiments, a particular layer 44 in themulti-layer coating 18 may be chiral such that the particular layer 44is ordered through orientation and/or chemical structure.

A multi-layer coating 18 on PCB 10 may have any suitable thickness 24.For example, a multi-layer coating 18 may have an overall thickness 24from one nm to ten μm, from one nm to five hundred nm, from three nm tofive hundred nm, from ten nm to five hundred nm, from ten nm to twohundred and fifty nm, or from ten nm to thirty nm. In a preferredembodiment, a multi-layer coating 18 on PCB 10 has an overall thickness24 from ten nm to one hundred nm, with one hundred nm being a preferredthickness 24.

The respective layers 44 within a multi-layer coating 18 may have anysuitable thickness. In some embodiments, the ratio of thicknesses ofeach layer 44 may be varied to achieve different properties of coating18. In some embodiments, each layer 44 within coating 18 on PCB 10 maybe of equal or approximately equal thickness. In other embodiments, onelayer 44 may be thicker than other layer(s) 44 so that a multi-layercoating 18 exhibits overall properties that are tuned to provide thecombined functionality derived from contributions from each layer 44within coating 18. According to certain embodiments, the thickness of aparticular layer 44 may comprise sixty to ninety percent of the overallthickness 24 of a multi-layer coating 18, and the combined thickness ofthe remaining layer(s) 44 may comprise ten to forty percent of theoverall thickness 24 of the multi-layer coating 18.

In embodiments where coating 18 comprises multiple graded layers 44, theproportions of the respective polymers in the graded layers 44 may bevaried to achieve different properties of the overall coating 18. Wherecoating 18 comprises multiple graded layers 44, adjacent layers 44 maybe fused together such that polymers of intermediate chemicalcomposition are present between adjacent layers 44. In addition, oralternatively, a multi-layer coating 18 may comprise one or more polymerlayers 44 adjacent to a layer 44 of metal halide (e.g., metal fluoride).According to certain embodiments, the proportion of each polymer in agraded, multilayer coating 18 may be equal. In other embodiments ofcoating 18 comprising graded layers 44 of different polymers, coating 18may comprise more of a particular polymer than other polymer(s) suchthat the multi-layer coating 18 more highly exhibits the properties ofthe particular polymer. In such embodiments, the particular polymer maymake up sixty to ninety percent of coating 18 such that the remainingpolymer(s) make up ten to forty percent of coating 18. As noted above,the interface between layers 44 may be well defined in some embodiments,and in other embodiments, the interface between layers 44 may be graded.

According to certain embodiments, the first layer 44 a of themulti-layer coating 18 (i.e., the particular layer 44 abutting substrate14 and/or conductive tracks 16) is continuous or substantiallycontinuous. In such embodiments, none or substantially none of thesecond layer 44 b may come into contact with substrate 14 and/orconductive tracks 16 of PCB 10. One or more layers 44 of the multi-layercoating 18 may be deposited on substrate 14 and/or conductive tracks 16prior to the soldering of any electrical components 12 to conductivetracks 16 on substrate 14. Accordingly, there may be no solder 38, oressentially no solder 38, between one or more layers 44 of themulti-layer coating 18 and conductive tracks 16.

As explained above, electrical components 12 may be connected toconductive tracks 16 by various methods such as, for example, solderingand or wire bonding. In some embodiments, at least one layer 44 of amulti-layer coating 18 may be optimized for wire bonding and anotherlayer of the multi-layer coating 18 may be optimized for soldering. Forexample, a first layer 44 that is optimized for wire bonding may befirst deposited on conductive tracks 16. The wire bonding process maythen be executed to connect at least one electrical component 12 toconductive track 16. A second layer 44 of the multi-layer coating 18 maythen be deposited over PCB 10. The second layer 44 may be optimized forsoldering. Another electrical component 12 may then be soldered throughthe multi-layer coating 18 to conductive track 16. Alternatively, theforegoing steps could be reversed such that the particular layer 44 thatis optimized for soldering could be deposited, then the soldering couldbe performed, then the particular layer 44 that is optimized for wirebonding could be deposited, and then the wire bonding could beperformed.

In some embodiments, coating 18 comprises at least one layer 44comprising a low-halogen-containing hydrocarbon polymer. Alow-halogen-containing hydrocarbon polymer may be any suitable polymerhaving less than a threshold quantity of halogen atoms. For example, alow-halogen-containing hydrocarbon polymer may refer to a polymer havingless than a configurable percentage (by mass) of halogen atoms (e.g.,less than two percent by mass, less than 0.5 percent by mass, and/or anysuitable percentage).

According to certain embodiments, coating 18 comprises at least onelayer 44 comprising a halo-hydrocarbon polymer and another layer 44comprising a non-halo-hydrocarbon polymer. In some embodiments, anon-halo-hydrocarbon polymer may be any suitable polymer that does notcomprise halogen atoms. A non-halo-hydrocarbon polymer may have astraight or branched chain or ring carbon structure. In someembodiments, there may be crosslinking between the chains of anon-halo-hydrocarbon polymer. A non-halo-hydrocarbon polymer maycomprise one or more unsaturated groups such as, for example,carbon-carbon double and/or triple bonds. In some embodiments, anon-halo-hydrocarbon polymer comprises one or more heteroatoms (i.e.,atoms that are not carbon, hydrogen, or a halogen) such as, for example,nitrogen, sulphur, silicon, and/or oxygen. According to certainembodiments, the molecular weight of a non-halo-hydrocarbon polymer isgreater than five hundred amu. A non-halo-hydrocarbon polymer may be apolymer that can be deposited by plasma deposition.

A particular layer 44 of coating 18 may comprise any suitablenon-halo-hydrocarbon polymer(s). For example, the particular layer 44may comprise a polyalkene, a polyester, a vinyl polymer, a phenolicresin, and/or a polyanhydride. In a preferred embodiment, the particularlayer 44 comprises a polyalkene such as, for example, polythene and/orpolypropylene.

In some embodiments, PCB 10 may comprise coating 18 comprising (i) afirst layer 44 a of a non-halo-hydrocarbon polymer that is depositeddirectly on substrate 14 and/or conductive tracks 16 and (ii) a secondlayer 44 b of a halo-hydrocarbon polymer that is deposited on the firstlayer 44 a. Such embodiments may be advantageous where a metal halidelayer 44 on conductive tracks 16 is not desirable. In particular,depositing a first layer 44 a of a non-halo-hydrocarbon polymer directlyon conductive tracks 16 may prevent the formation of a metal halidelayer 44 on conductive tracks 16. In some embodiments, a metal halidelayer 44 may be undesirable if it results, for example, inintermetallics that are vulnerable to weakening under specificenvironmental conditions. In such embodiments, a first layer 44 acomprising a non-halo-hydrocarbon polymer may serve as a barrier betweenconductive tracks 16 and a second layer 44 b comprising ahalo-hydrocarbon polymer. Thus, the formation of a first layer 44 acomprising a non-halo-hydrocarbon polymer may prevent the formation of ametal halide layer 44 during subsequent deposition of a layer 44comprising a halo-hydrocarbon polymer.

In other embodiments, a metal halide layer may be desired. In suchembodiments, coating 18 may comprise (i) a first layer 44 a of a metalhalide that is formed directly on substrate 14 and/or conductive tracks16 and (ii) a second layer 44 b of a halo-hydrocarbon polymer that isdeposited on the first layer 44 a.

Although one or more embodiment described above comprise a first layer44 a of a non-halo-hydrocarbon polymer and a second layer 44 b of ahalo-hydrocarbon polymer, it should be understood that, in otherembodiments, all, some, or none of the layers 44 of a multi-layercoating 18 may comprise a halo-hydrocarbon polymer. It should be furtherunderstood that all, some, or none of the layers 44 of the multi-layercoating 18 may comprise a non-halo-hydrocarbon polymer.

A multi-layer coating 18 on PCB 10 may be configured to offer varyingand/or customized performance. In some embodiments, layers 44 of amulti-layer coating 18 may be configured to optimize the conductivity,oxidation resistance, environmental protection, cost, moistureabsorption/resistance, dendrite prevention, flame retardancy, and/orother optical, electrical, physical, and/or chemical properties of themulti-layer coating 18. For example, a relatively thick coating 18 thatis highly fluorinated may be desirable to provide good environmentalprotection in certain embodiments, while in other embodiments, arelatively thin coating 18 comprising less halide may be preferred. Asdescribed above with respect to FIGS. 3A-B, electrical components 12 maybe soldered through a multi-layer coating 18 to conductive tracks 16without first removing the multi-layer coating 18.

According to certain embodiments, a multi-layer coating 18 on PCB 10comprises a first layer 44 a comprising a first type of halo-hydrocarbonpolymer and a second layer 44 b comprising a second type ofhalo-hydrocarbon polymer. In some embodiments, a multi-layer coating 18comprises a particular layer 44 of a polytetrafluoroethylene (PTFE) typematerial and another layer 44 of a polychlorotrifluoroethylene (PCTFE)type material. The PCTFE layer 44 may be deposited directly on substrate14 and/or conductive tracks 16 and the PTFE layer 44 may be deposited onthe PCTFE layer 44. In such embodiments, the PCTFE layer 44 may preventoxidation of conductive tracks 16 and the PTFE layer 44 may provideenvironmental protection for PCB 10. In other embodiments, the PTFElayer 44 may be deposited directly on substrate 14 and/or conductivetracks 16 and the PCTFE layer 44 may be deposited on the PTFE layer 44.This may allow the external physical and/or chemical properties of thesurface of PCB 10 to be determined by the PCTFE layer 44.

Although FIG. 4 illustrates a multi-layer coating 18 having distinctlayers, it should be understood that the multi-layer coating 18 may havegraded layers. Although a PTFE layer 44 and a PCTFE layer 44 of amulti-layer coating 18 are described above, it should be understood thatthe multi-layer coating 18 may comprise any suitable types and/orcombinations of materials. In some embodiments, the material(s) in themulti-layer coating 18 may not be PTFE type and/or PCTFE type materials.

FIG. 5 illustrates PCB 10 comprising a multi-layer coating 18selectively applied to particular regions of PCB 10, according tocertain embodiments. As illustrated, particular regions of PCB 10 may becoating 18 with a single-layer coating 18 and other regions of PCB 10may be coated with a multi-layer coating 18. Thus, different regions ofPCB 10 may be coated with different polymers, or mixtures thereof, toachieve different properties in the different regions. For example, in afirst region of PCB 10 it may be desirable to have a multi-layer coating18 that exhibits piezo-electric and/or electroresistive properties,while in a second region of PCB 10 it may be desirable to have asingle-layer coating 18 that exhibits electrically insulatingproperties. In this example, one may apply to the first region of PCB 10a multi-layer coating 18 having a first layer 44 a comprising a polymerof vinylidenefluoride (PVDF) and a second layer 44 b comprising anotherhalo-hydrocarbon polymer. Layer 44 of PVDF may enhance thepiezo-electric, electroresistive, and/or electrostrictive properties ofcoating 18 in the first region of PCB 10. In this example, one may applyto the second region of PCB 10 a single-layer coating 18 comprising ahalo-hydrocarbon polymer or a non-halo-hydrocarbon polymer that exhibitsgreater insulation properties that PVDF. Thus, particular regions of PCB10 may be coated with a single-layer coating 18 and other regions of PCB10 may be coated with a multi-layer coating 18.

Although the foregoing example illustrates coating 18 comprising PVDF,it should be understood that any suitable polymers may be used in anysingle-layer and/or multi-layer coating 18.

A multi-layer coating 18 may be applied to PCB 10 using any suitabletechnique. For example, a multi-layer coating 18 may be deposited usingplasma deposition, chemical vapour deposition (CYD), molecular beamepitaxy (MBE), plasma enhanced-chemical vapour deposition (PE-CYD), highpressure/atmospheric plasma deposition, metallo-organic-chemical vapourdeposition (MO-CYD), and/or laser enhanced-chemical vapour deposition(LE-CVD). In some embodiments, a multi-layer coating 18 may be depositedby the creation of inter-penetrating polymer networks (IPNs) and/or bysurface absorption of monolayers (SAMs) of polymers or monomers to formin-situ polymers and/or polymer alloys. In other embodiments, amulti-layer coating 18 may be deposited using a liquid coating techniquesuch as, for example, liquid dipping, spray coating, spin coating,sputtering, and/or a sol-gel process. In embodiments comprisingmulti-layer coatings 18, each layer 44 may be formed using the same ordifferent techniques.

In some embodiments, a multi-layer coating 18 is applied to PCB 10 usingthe plasma deposition technique described above with respect to FIG. 2.In such embodiments, once conductive tracks 16 are formed on substrate14, substrate 14 may be placed in chamber 30 in reactor 28. Reactor 28may introduce gases (e.g., hydrogen, argon, and/or nitrogen) intochamber 30 to clean substrate 14. Reactor 28 may then introduce one ormore precursor compounds 36 into chamber 30 to form a multi-layercoating 18 on substrate 14 by plasma deposition. In some embodiments,the multi-layer coating 18 may follow the three dimensional form ofsubstrate 14 and/or conductive tracks 16 of PCB 10.

A multi-layer coating 18 (comprising either distinct or graded layers44) may be deposited on substrate 14 by varying the composition ofprecursor compounds 36 introduced into chamber 30. In some embodiments,one or more precursor compounds 36 may be used to generate a gas mixturein chamber 30. The mixture of precursor compounds 36 may be configuredto generate graded layers 44 of coating 18 on substrate 14. In otherembodiments, distinct layers 44 of coating 18 may be deposited onsubstrate 14 by switching between precursor compounds 36 and modifyingconditions in chamber 30. The composition of a multi-layer coating 18may be controlled by one or more of the following factors: (i) theplasma gas selected; (ii) the particular precursor compound(s) 36 used;(iii) the amount of precursor compound(s) 36 (which may be determined bythe combination of the pressure of precursor compound(s) 36 and flowrate); (iv) the ratio of precursor compound(s) 36; (v) the sequence ofprecursor compound(s) 36; (vi) the plasma pressure; (vii) the plasmadrive frequency; (viii) the pulse width timing; (ix) the coating time;(x) the plasma power (including the peak and/or average plasma power);(xi) the chamber electrode arrangement; (xii) the preparation of theincoming PCB 10; and/or (xiii) the size and geometry of chamber 30.Coating 18 deposited by plasma deposition may completely, orsubstantially completely, encapsulate all surfaces of PCB 10. As aresult, coating 18 may stop or reduce aqueous absorption and “wetting”of PCB 10. This may significantly reduce any corrosive action fromwithin substrate 14 and/or from under or adjacent to conductive tracks16. This may be especially advantageous for epoxy-based PCBs 10 andpaper/card PCBs 10, which may tend to absorb water, aqueous acids,and/or corrosive materials and which may be vulnerable to corrosion bysuch in-situ mechanisms.

Plasma deposition may be used to deposit layer(s) 44 of halo-hydrocarbonpolymers and/or layer(s) 44 of non-halo-hydrocarbon polymers. Precursorcompounds 36 for halo-hydrocarbon polymers are described above withrespect to FIG. 2. With respect to non-halo-hydrocarbon polymers,precursor compounds 36 may be hydrocarbon materials that are selected toprovide the desired coating 18 properties. When introduced into the gasplasma, the particular precursor compounds 36 may be ionized/decomposedto generate a range of active species that will react at the surface ofPCB 10 (e.g., by a polymerisation process) to generate a thin layer 44of a non-halo-hydrocarbon polymer. Any suitable precursor compounds 36may be used to form a non-halo-hydrocarbon layer 44. Examples ofprecursor compounds 36 for depositing layer 44 of a non-halo-hydrocarbonpolymer are alkanes, alkenes, and alkynes.

As explained above, PCB 10 may be coated with complex, three-dimensionalcoatings 18. Such coatings 18 may comprise a single layer 44 overparticular regions of PCB 10 and multiple layers 44 over other regionsof PCB 10. Any suitable techniques may be used to form such coatings 18.In some embodiments, one or more layers 44 of coating 18 may bedeposited only on selective areas of PCB 10. For example, one or morelayers 44 of coating 18 may be selectively deposited (i) by masking thesurface of PCB 10 to deposit coating 18 only in non-masked areas, (ii)by using photo-assisted plasma deposition techniques (e.g., laser or UVlight assisted), and/or (iii) by using metallo-organic chemical vapourdeposition (MOCVD) type precursor compounds 36 such as, for example,metal-alkyl and/or carbonyl precursors. In other embodiments, coatings18 may be formed using one or more subtractive techniques.

According to certain embodiments, the deposition process may beconfigured to modify the wetting characteristics of coating 18 on PCB10. Wetting may refer to (i) the wetting of the surface of the coatedPCB 10 by liquids such as water, (ii) the wetting of coating 18 bysolder 38 and/or flux 42 during the soldering process, and/or (iii) thewetting of conductive tracks 16 by solder 38 after coating 18 has beenaltered (e.g., locally removed). The wetting characteristics of coating18 may be modified according to any suitable technique. For example, thewetting characteristics of coating 18 may be modified by plasma etchingusing reactive gas plasmas such as, for example, carbon tetrafluoride(CF₄). As another example, the wetting characteristics of coating 18 maybe modified by plasma activation using gas plasmas selected to providethe desired surface activation such as, for example, gas plasmas basedon hydrogen, oxygen, argon, nitrogen, and/or combinations of such gases.As yet another example, the wetting characteristics of coating 18 may bemodified by plasma polymerisation and/or by using variants of and/ormixtures of halo-hydrocarbons (e.g., fluoro-hydrocarbons,chloro-hydrocarbons, etc.) and/or non-halo-hydrocarbons (e.g.,polyethylene, polypropylene, etc.). As yet another example, the wettingcharacteristics of coating 18 may be modified by liquid based chemicaletching, which may modify the surface activation and/or surfaceroughness of coating 18 using, for example, strong acids (e.g.,sulphuric acid, nitric acid, etc.) and/or oxidizing agents (e.g.,hydrogen peroxide). In some embodiments, the wetting characteristics ofcoating 18 may be spatially controlled to provide different regions ofPCB 10 having different wetting characteristics. A region (on thesurface of PCB 10) that has enhanced wetting characteristics mayselectively control the direction in which liquid flows across PCB 10.Thus, such a region may act as a “gutter” to direct liquid runoff toareas where the liquid will not cause damage.

In some embodiments, some or all surfaces of PCB 10 may be completely orsubstantially encapsulated with coating 18. This may protect PCB 10and/or prevent aqueous absorption and/or “wetting” of PCB 10. Inaddition, or alternatively, this may reduce any corrosive action fromwithin substrate 14 or from under or adjacent to conductive tracks 16.Thus, coating 18 may protect PCB 10 having an epoxy-based, paper-based,and/or card based substrate 14 which would otherwise absorb liquids(e.g., water, aqueous acids, and corrosive materials) and which mayotherwise be vulnerable to corrosion.

PCB 10 comprising coating 18 may provide advantages over uncoated PCBs10. The disclosed coating 18 may provide none, some, or all of thefollowing advantages. One advantage is that, in some embodiments,coating 18 may permit PCB 10 to operate in harsh and/or corrosiveenvironments. Traditional PCBs 10 have generally been unable to reliablyfunction in such environments. Conductive tracks 16 on uncoated PCBs 10may corrode, which may result in a far shorter lifetime of the devicethan would normally be expected. This may occur, for example, when anuncoated PCB 10 is used in very humid environments, especially wheremicroscopic droplets of water comprising dissolved gases such as sulphurdioxide, hydrogen sulphide, nitrogen dioxide, hydrogen chloride,chlorine, ozone, and/or water vapour form a corrosive solution. This maylead to a thin film or corrosion deposit forming between conductivetracks 16 on the uncoated PCB 10, which may cause short circuits. Insome cases, manufacturers have applied conformal coatings of a polymerto PCB 10 after soldering electrical components 12 to PCB 10. However,such conformal coatings are generally expensive. Applying such conformalcoatings may require an extra step in the manufacturing process afterelectrical components 12 have been soldered to PCB 10. Such conformalcoatings may also require another step to remove the conformal coatingwhen it is necessary to rework a damaged or failed PCB 10 or when it isnecessary to test PCB 10 to ascertain its performance or troubleshoot aproblem. In contrast to such conformal coatings, coating 18 comprising ahalo-hydrocarbon polymer may represent a lower cost and/or higherperformance solution for protecting PCB 10 in harsh and/or corrosiveenvironments. In some embodiments, one or more layers 44 of coating 18may be applied in a conformal fashion to PCB 10 after attaching (e.g.,soldering, wire bonding, etc.) electrical components 12 to conductivetracks 16. Thus, coating 18 may be applied to a populated PCB 10 as aconformal coating 18 that provides one or more advantages describedherein (e.g., oxidation/corrosion resistance, solder-through capability,wire bonding capability, z-axis conductivity, etc.).

Another advantage is that, in some embodiments, coating 18 may preventsubstrate 14, conductive tracks 16, and/or other elements of PCB 10 fromabsorbing water and/or solvents. The elements of traditional PCBs 10 maycomprise materials that absorb water and/or solvents (including aqueous,organic, inorganic, and/or mixed solvents) in liquid, vapour, and/orgaseous form. For example, substrates 14 comprising fabrics (e.g., epoxyresin bonded glass fabrics), paper (e.g., synthetic resin bonded paper,cotton paper, phenolic cotton paper, epoxy, paper, cardboard, etc.),textiles, and/or wood based materials (natural and/or synthetic) mayabsorb water and/or solvent-based chemicals. As another example,conductive tracks 16 comprising metals, conductive polymers, and/orprinted conductive inks may absorb water and/or solvent-based chemicals.As yet another example, PCB 10 may comprise magnetic structures, printedmagnetic inks, and/or other elements that may absorb water and/orsolvent-based chemicals. Thus, PCB 10 may comprise porous and/orhydrophilic structures having a natural tendency for water and/orsolvents that may cause changes to those structures. (The tendency of amaterial to interact with water and/or solvents in the liquid phase orthrough condensation from the gas phase may include solid solvents.)When elements of PCB 10 absorb water and/or solvents, one or moreproblems may result. These problems may include: (i) increasedmechanical stresses during thermal cycles due to differences in thermalexpansion coefficients; (ii) alteration of adhesion properties of PCBelements; (iii) alterations to the dielectric constant and loss tangentof PCB elements; (iv) swelling of the structure rendering some materialsunsuitable for plated through holes and/or for use in some high humidityconditions, especially where high voltages are used; (v) corrosion ofconductive tracks 16 at or around the interface between conductivetracks 16 and substrate 14; (vi) loss of mechanical strength; (vii)reordering of material in PCB 10 in the presence of water; and/or (viii)electrolysis in the presence of an applied field leading to corrosionand/or degradation of PCB 10.

Another advantage may be realized where conductive tracks 16 comprise aconductive ink polymer. Conductive ink polymers may tend to absorbliquids and/or moisture, which may result in swelling, modification ofelectrical properties, and/or degradation of circuit performance. Inaddition, or alternatively, printed active devices (e.g., as used inplastic electronics) may absorb water and/or solvent-based chemicals,which may change the performance and/or properties of printed activedevices. Applying coating 18 to printed active devices and/or conductivetracks 16 comprising conductive ink polymers may prevent waterabsorption.

In some embodiments, coating 18 may be configured to exhibitconductivity along an axis pointing into the plane of the coated surface(the “z-axis” 22) while acting as an insulator along the axes parallelto the coated surface (the “x-axis” 46 and the “y-axis” 48).Accordingly, coating 18 may be applied to a conductive contact 50without hindering the ability of such contact 50 to transmit anelectrical signal and/or carry current to a mating contact 50. Thus, insome embodiments, coating 18 may protect contacts 50 from oxidationand/or corrosion without hindering the conductivity of contacts 50.

FIGS. 6A-B illustrate a keypad 52 comprising contacts 50 that are coatedwith coating 18, according to certain embodiments. Keypad 52 may be aninput device comprising a plurality of keys 54. By depressing key 54,user may cause keypad 52 to transmit an electrical signal. Keypad 52 maybe any suitable type of input device that comprises keys 54. Forexample, keypad 52 may be a dome-switch keypad 52, a membrane keypad 52,and/or any suitable keypad 52.

Keypad 52 may comprise a plurality of keys 54. In some embodiments, eachkey 54 comprises an exposed surface 56 that is visible to a user and aconcealed surface 58 that is generally not visible to the user. Aconductive contact 50 may be attached to the concealed surface 58 ofeach key 54 in keypad 52. In some embodiments, keypad 52 comprises PCB10 having a plurality of conductive contacts 50. Each contact 50 on PCB10 may correspond to one or more keys 54 of keypad 52. Thus, when a userdepresses a particular key 54, contact 50 attached to key 54 may touchthe corresponding contact 50 attached to PCB 10, thus allowing anelectrical signal to flow (e.g., by closing an open circuit).

Keypad 52 may comprise any suitable type of keys 54. Examples of keys 54include metal “snap dome” keys 54, spring actuated keys 54, and siliconrubber buttons having one or more carbon inserts. In some embodiments,key 54 may represent an area of a membrane keypad 52. A membrane keypad52 may comprise two membrane layers (e.g., plastic or polymersubstrates) that are normally separated by an air space. The innersurfaces of the two membranes may comprise flexible contacts 50 such as,for example, conductive inks (e.g., silver ink), conductive glues,and/or conductive adhesives. The depression of key 54 of a membranekeypad 52 may cause contacts 50 of the two membranes to touch, resultingin transmission of a signal. It should be understood that keypad 52 maycomprise any suitable type and/or combination of keys 54.

Contact 50 in keypad 52 may be any suitable conductive device forjoining and/or closing an electrical circuit. Contact 50 may comprise anelectrode, connector, pin, pad, and/or any suitable conductive device.Contact 50 may comprise any suitable conductive material. For example,contacts 50 may comprise one or more metals such as, for example,stainless steel, nickel, tin, copper, aluminium, gold, silver, and/orany suitable alloy thereof. In some embodiments, contacts 50 maycomprise conductive inks, silver loaded epoxy, conductive plastics,and/or nonmetallic conductive materials such as, for example, carbonand/or graphite. Thus, contacts 50 may comprise any suitable type and/orcombination of conductive materials.

In some embodiments, one or more contacts 50 in keypad 52 may be coatedwith coating 18. As explained above, coating 18 may be configured to beelectrically conductive in the z-axis direction but to act as aninsulator in the x-axis and y-axis directions. In other words, coating18 may exhibit higher impedance and/or resistance in the x-axis andy-axis directions but low impedance and/or resistance in the z-axisdirection. This property may allow contact 50 coated with coating 18 toconduct an electrical signal and/or current through coating 18 to amating contact 50.

Coating 18 on contact 50 in keypad 52 may have any suitable thickness24. In some embodiments, thickness 24 of coating 18 on contact 50 isfrom one nm to two μm. In other embodiments, thickness 24 of coating 18may be from one nm to five hundred nm. In yet other embodiments,thickness 24 of coating 18 may be from three nm to five hundred nm. Inyet other embodiments, thickness 24 of coating 18 may be from ten nm tofive hundred nm. In yet other embodiments, thickness 24 of coating 18may be from ten nm to two hundred and fifty nm. In yet otherembodiments, thickness 24 of coating 18 may be from ten nm to thirty nm.In yet other embodiments, coating 18 is a monolayer of ahalo-hydrocarbon polymer (having thickness 24 of a few angstroms (Å)).In a preferred embodiment, thickness 24 of coating 18 is from ten nm toone hundred nm in various gradients, with one hundred nm being apreferred thickness 24.

In some embodiments, the optimal thickness 24 of coating 18 may dependon the coating properties that are desired. For example, if very highenvironmental toughness is required (e.g., high corrosion and abrasionresistance), a thicker coating 18 may be preferred. In some embodiments,thickness 24 of coating 18 may be optimised with different thicknesses24 at different locations of the device, depending on Which propertiesare being optimised (e.g., environmental protection versus z-axisconductivity). Coating 18 may be optimised for compliance to avoidcracking when flexed; to minimise wear on coating 18 and/or wear causedby coating 18; for environmental protection; for physical protection ofa softer, underlying material; for controlled resistance for circuittrimming; for stability for reference measurements ofsensors/electrodes; and/or for surface energy, charge dissipation,and/or blooming.

As noted above, contact 50 coated with coating 18 may conduct anelectrical signal and/or current through coating 18 to a mating contact50. In this context, the phrase “conduct through” may refer toconducting an electrical signal and/or current between two or morecontacts 50 without removing coating 18. Thus, coating 18 may bedeposited between at least two mating contacts 50 and then a signaland/or current may be conducted between the mating contacts 50 withoutremoving coating 18. The ability to conduct a signal and/or currentthrough coating 18 may be due at least in part to the low impedanceand/or resistance of coating 18 in the z-axis direction. Thus, thephrase “conduct through” may refer to conducting an electrical signaland/or current between two or more contacts 50 without removing coating18.

The conductivity of coating 18 may be measured according to any suitabletechnique. In some embodiments, the conductivity of coating 18 may bemeasured by determining the resistance of coating 18. Such measurementmay be achieved by soldering conductive wires to contacts 50 andconnecting wires to a resistance meter 60. A predetermined force 62 maycause contacts 50 to touch each other (e.g., be brought into electricalcontact). As illustrated in FIG. 6B, resistance meter 60 may thenmeasure the resistance through coating 18 between the correspondingcontacts 50. As a reference point, the resistance of contacts 50themselves may be determined by measuring the resistance betweenuncoated contacts 50. According to certain embodiments, coating 18 mayexhibit z-axis resistance in a range from zero to ten kilo-ohms (ill).In a preferred embodiment, coating 18 may exhibit z-axis resistance in arange from zero to one ohms (n).

FIG. 7 is a graph 64 illustrating the z-axis resistance of examplecoatings 18 having various thicknesses 24, according to certainembodiments. The metrics illustrated in graph 64 are example values ofz-axis resistance for example coatings 18. It should be understood,however, that coatings associated with different materials, structures,deposition techniques, and/or other factors may exhibit differentamounts of z-axis conductivity. Although graph 64 illustrates z-axisresistance in relation to thickness 24, it should be understood thatother variables (e.g., materials, structure, deposition method, etc.)may affect the z-axis conductivity of coating 18.

In the illustrated example, the z-axis resistance of an example coating18 on keypad 52 was measured using resistance meter 60, as illustratedin FIG. 6B. Contacts 50 in this example were coated with a PTFE typematerial. A metal “snap-dome” key 54 was used as one of contacts 50.Electrical wires were soldered to contacts 50 and connected toresistance meter 60. A predetermined force 62 (approximately five Newtonmeters) was applied to one contact 50, causing that contact 50 to toucha corresponding contact 50. Resistance meter 60 then measured theelectrical resistance between the touching contacts 50. Thepredetermined force 62 was applied by using ENIG plated tracks and byvarying force 62 until a stable resistance measurement was made. Themeasurement was repeated for coatings 18 of different thicknesses 24.The resulting readings were adjusted to account for (i) the fact thattwo thicknesses 24 of coating 18 (i.e., one thickness 24 for eachcontact 50) were present in the measurement path and (ii) the resistanceof the particular contacts 50 without coating 18. The resistance ofcontacts 50 was determined by using an uncoated PCB 10 as a reference.

The results of these measurements are illustrated in graph 64 in FIG. 7and in the table below. Graph 64 in FIG. 7 comprises a first axis 66that corresponds to the resistance of coating 18 and a second axis 68that corresponds to thickness 24 of coating 18. The measured resistancesare illustrated as points 70 in graph 64.

Coating thickness Resistance of coating (nm) (Ω) 30 0.0704 40 0.1688 500.2095 75 0.4105 200 1.2775

Although the foregoing example illustrates the resistance of aparticular coating 18 comprising a PTFE type material, it should beunderstood that coating 18 may comprise any suitable type and/orcombination of halo-hydrocarbon polymers. Although the foregoing exampleillustrates the resistance of coating 18 having particular thicknesses24, it should be understood that coating 18 may be configured to haveany suitable thickness 24.

Generally, contacts 50 in a device may be coated with coating 18 beforeor after construction of the device. In a preferred embodiment, contacts50 are coated with coating 18 before construction of the device. Coating18 may be applied to one, some, or all of the surfaces of contact 50. Insome embodiments, coating 18 may be applied to one or more surfaces ofthe device (e.g., keypad 52). Coating 18 may be applied to surfaces ofcontact 50 and/or device that will be exposed to the environment suchas, for example, surfaces that act as electrical contact areas betweentwo or more parts of a circuit. Applying coating 18 to the surfaces ofdevice in addition to the surfaces of contact 50 may (i) increase theprotection of the device from corrosion and/or oxidation and/or (ii)prevent the formation of spoilage routes to contact areas in device.

Coating 18 may be deposited on contacts 50 according to any suitabletechnique. For example, coating 18 may be deposited using chemicalvapour deposition (CVD), molecular beam epitaxy (MBE), plasmaenhanced-chemical vapour deposition (PE-CVD), high pressure/atmosphericplasma deposition, metallo-organic-chemical vapour deposition (MO-CVD),and/or laser enhanced-chemical vapour deposition (LE-CVD). In someembodiments, coating 18 may be deposited on contacts 50 by the creationof inter-penetrating polymer networks (IPNs) and/or by surfaceabsorption of monolayers (SAMs) of polymers or monomers to form in-situpolymers and/or polymer alloys. In other embodiments, coating 18 may bedeposited using a liquid coating technique such as, for example, liquiddipping, spray coating, spin coating, sputtering, and/or a sol-gelprocess.

According to certain embodiments, coating 18 may be deposited oncontacts 50 using plasma deposition, as described above with respect toFIG. 2. Thus, contacts 50 may be placed in chamber 30 in reactor 28.Reactor 28 may then introduce gases (e.g., hydrogen, argon, and/ornitrogen) into chamber 30 to clean contacts 50. In one or more steps,reactor 28 may then introduce one or more precursor compounds 36 intochamber 30 to form a single-layer or multi-layer coating 18 on contacts50 by plasma deposition. In some embodiments, coating 18 may follow thethree dimensional form of contact 50. The preferred method fordepositing coating 18 on contacts 50 may depend on the particularthickness 24 of coating 18 that is desired. Liquid coating techniquesmay be preferred for thicker coatings 18, while plasma deposition may bepreferred for thinner coatings 18.

The technique used to deposit coating 18 on contacts 50 may beconfigured to control the z-axis conductivity of coating 18. In someembodiments, the z-axis conductivity of coating 18 may be controlled byregulating one or more of the following factors:

-   -   Composition of halo-hydrocarbon material in coating 18, which        may include combining different halo-hydrocarbon materials and        controlling the gradation between layers 44 of the different        materials.    -   Ratios of halogen atoms/hetero-atoms/carbon atoms In the        halo-hydrocarbon material in coating 18.    -   Proportion of carbon in the halo-hydrocarbon coating material.    -   Degree of conjugation in the halo-hydrocarbon coating material.    -   Average molecular weight of the halo-hydrocarbon coating        material.    -   Degree of branching and cross-linking in the halo-hydrocarbon        coating material.    -   Molecular size distribution of molecules in the halo-hydrocarbon        coating material.    -   Density of the halo-hydrocarbon coating material.    -   Presence of additional doping agents in the halo-hydrocarbon        coating material.    -   Presence of ionic/salt, ionic, and/or covalent components In the        halo-hydrocarbon coating material.    -   Presence of organic/polymer and inorganic compounds comprising        transition metals, including complex cations and anions in the        halo-hydrocarbon coating material.    -   Presence of compounds and/or elements having variable oxidation        states in the halo-hydrocarbon coating material.    -   Presence of chemical compounds having delocalized character in        the halo-hydrocarbon coating material.    -   Presence of occluded components in the halo-hydrocarbon coating        material.    -   When coating 18 is deposited by plasma deposition, adjustment of        plasma conditions (e.g. power, gas pressure, electrode        arrangement).    -   Thickness of the halo-hydrocarbon coating material (e.g.,        thicker coatings 18 may exhibit greater resistance than thinner        coatings 18 of the same material).    -   Orientation of coating 18.    -   Continuity of coating 18 (e.g., porosity and/or        three-dimensional structure).

Although keypad 52 is described in the examples above, coating 18 may beapplied to contacts 50 in any type of device. For example, coating 18may be applied to contacts 50 in safety switches, alarm switches, fuseholders, keypads 52 on mobile telephones, touch screens, batteries,battery terminals, semiconductor chips, smart cards, sensors, testchips, elastomeric connectors (e.g., Zebra strips), electricalconnectors (e.g., sockets and plugs), terminators, crimped connectors,press-fit connectors, and/or sliding contacts 50 such as, for example,those used in chips, smart cards, tokens, and/or reader mechanisms.

FIG. 8 illustrates a measuring device 72 comprising a sensor 74 havingcoated contacts 50, according to certain embodiments. Sensor 74 may beany suitable type of sensor 74. In some embodiments, sensor 74 is adisposable sensor 74 that measures analytes such as, for example, toxicgases, glucose, physiological fluid-based chemical compounds, and/orother chemical compounds. Sensor 74 may comprise a membrane 76, one ormore electrodes 78, one or more contacts 50, and a sensor substrate 80.Membrane 76 may be any suitable material that filters a fluid to allowanalytes to reach electrodes 78. In some embodiments, membrane 76 may bea biocompatible membrane. Thus, analytes may diffuse through membrane 76and react at an electrolyte-catalyst interface, which may create anelectrical current.

Electrodes 78 in sensor 74 may comprise a catalyst and/or other materialconfigured to interact with analytes. For example, electrode 78 may be aenzyme electrode comprising glucose oxidase and/or dehydrogenase. Theinteraction of analytes with electrode 78 may generate a signal that iselectrical or may be converted into an electrical signal. One or morecontacts 50 in sensor 74 may transmit the electrical signal to the mainbody 82 of measuring device 72. In some embodiments, contacts 50 onelectrodes 78 are in electrical contact with the main body 82 ofmeasuring device 72 such that an electrical circuit is made with themain body 82 of measuring device 72. In some embodiments, the totalcharge passing through contacts 50 may be proportional to the amount ofanalytes in the fluid that has reacted with the enzyme at electrode.Measuring device 72 may be configured and/or calibrated to measure thesignal from contacts 50 and to report the presence and/or concentrationof analytes.

Electrodes 78 may be affixed to and/or printed on sensor substrate 80.In some embodiments, sensor 74 may comprise a power source coupled toelectrodes 78. Sensor 74 may be configured to detect analytes in a gasand/or liquid state.

Contacts 50 in sensor 74 may comprise any suitable material. In someembodiments, contacts 50 comprise a soft contact material such as, forexample, carbon, conductive inks, and/or silver loaded epoxy. In someembodiments, contact 50 in sensor 74 may make electrical contact withanother contact 50 in the main body 82 of measuring device 72, thusforming a circuit between sensor 74 and the main body 82 of measuringdevice 72. Contacts 50 may be coated with coating 18 of any suitablethickness 24 (e.g., from one nm to two μm). One or more contacts 50 insensor 74 may be uncoated.

In some embodiments, the main body 82 of measurement device is reusablewhile sensor 74 is disposable (e.g., only used once). In otherembodiments, sensor 74 may be a multi-use sensor 74 or otherwisedesigned for a long lifetime. The connection between the main body 82 ofmeasurement device and sensor 74, through contacts 50, may bereproducible and/or may provide a constant or essentially constantresistance. As noted above, contacts 50 may comprise a soft contactmaterial such as, for example, carbon, conductive inks, and/or silverload epoxy. Without coating 18, particles from these soft materialscould break away from contacts 50 and accumulate on components withinthe main body 82 of measuring device 72. By applying coating 18 tocontacts 50, however, one may prevent these soft materials from breakingaway from contacts 50 and accumulating on components in the main body 82of measuring device 72.

Although the foregoing example describes applying coating 18 to contacts50 of an analyte sensor 74, it should be understood that coating 18 maybe applied to contacts 50 or other components of any type of sensor 74or suitable other device. For example, coating 18 may be applied to anysuitable device or system where soft (e.g., carbon) pads are used tomake a repeated electrical connection. Such systems may use the samesensor 74 many times or may use the same device repeatedly withdisposable sensors 74.

In some embodiments, coating 18 on contact 50 of a device may comprise avery thin layer (e.g., five nm or less) of metal halide (preferably ametal fluoride) directly on the surface of contact 50. In someembodiments, the metal halide layer may be a monolayer, substantially amonolayer, or a few monolayers. In other embodiments, the metal halidelayer may comprise a metal halide zone of layers at the surface ofcontact 50. The metal halide layer on contact 50 may be robust, may beinert, and/or may prevent the formation on contact 50 of oxide layersand/or other tarnishes which may prevent effective electrical contact orsubsequent processing.

In embodiments where coating 18 is applied by plasma deposition, a metalhalide layer may form on contact 50 when active species in the gasplasma react with the metal surface of contact 50. In some embodiments,the metal halide layer may be enhanced using a higher concentration offluorine species. A layer of coating 18 comprising a halo-hydrocarbonpolymer may then be deposited on and/or In combination with the metalhalide layer. The metal halide layer and the layer of halo-hydrocarbonpolymers may be discrete, axially or spatially. Alternatively, there maybe a graded transition from metal halide to halo-hydrocarbon polymer incoating 18 on contact 50. In some embodiments, the metal halide layermay protect contact 50 from oxidation while the layer ofhalo-hydrocarbon polymers (i) may provide environmental protection fromcorrosive gases and/or liquids and/or (ii) may provide oxidationprotection. Should the layer of halo-hydrocarbon polymers in coating 18eventually be worn away by mechanical abrasion, the underlying metalhalide layer may prevent oxidation build-up, thus enabling contact 50 tocontinue to make an electrical connection.

In some embodiments, the surface properties of coating 18 may beconfigured to permit components to be bonded to the surface of coating18. For example, coating 18 may be configured to permit adhesion betweenthe surface of coating 18 and electrical components 12. In someembodiments, the annealing and/or thermal properties of coating 18 maybe configured such that one or more layers 44 of coating 18 may beselectively removed from a coated device.

Applying coating 18 to contacts 50 may provide advantages overtraditional devices. Coating 18 may provide none, some, or all of thefollowing advantages. One advantage is that coating 18 may prolong thelife of contacts 50 by protecting them from environmental damage and/orcorrosion. Some devices are typically used in very humid environments.In such environments, microscopic droplets of water comprising dissolvedgases (e.g., sulfur dioxide, hydrogen sulfide, nitrogen dioxide,hydrogen chloride, chlorine, ozone, and/or water vapour) may form acorrosive solution. Such droplets of moisture may form a thin film ordeposit of corrosion on contacts 50 in a device. Such corrosion maydegrade and shorten the useful life of contacts 50. Traditional coatingsubstances such as, for example, traditional polymers and plastics arenormally insulators and have therefore proven to be unsuitable forcoating contacts 50. Coating 18 comprising halo-hydrocarbon polymers,however, may exhibit conductivity in the z-axis direction. Accordingly,coating 18 may not hinder the ability of contacts 50 to receive and/ortransmit signals. In addition, or alternatively, where contacts 50 arecoated with coating 18, contacts 50 may be protected from corrosion.

Another advantage is that coating 18 may preserve the integrity of thesurface of contacts 50. As explained above, corrosion and/or oxidationof contacts 50 may prevent and/or interfere with the ability of contacts50 to make electrical connection with each other. This problem may occurwhere the corrosion and/or oxidation causes the formation of aninsulating layer over the surface of contacts 50 and/or a physicalchange to the surface of contacts 50 which prevents contacts 50 frommaking good electrical contact with each other. This problem may arise,for example, where an uncoated contact 50 is a safety switch orconnector for an alarm system. Such systems are frequently inactive forlong periods of time but should function correctly when required.Uncoated contacts 50 may become disconnected where the corrosion formsan insulating barrier between the mating contacts 50 such as, forexample, in fuse holders and battery terminals. Where contacts 50 arecoated with coating 18, however, contacts 50 may be protected fromcorrosion and/or oxidation. Thus, coating 18 may preserve the surfaceintegrity of contacts 50.

Another advantage is that coating 18 may protect contacts 50 fromcorrosion. In devices comprising uncoated contacts 50, corrosion mayprevent movement of contacts 50 that are designed to move. In somecases, corrosion may change the resistance/performance of a circuitand/or degrade removable elements of a device. Where contacts 50 arecoated with coating 18, however, contacts 50 may be protected fromcorrosion, thereby extending the life of a device comprising contacts50.

As explained above, electrical component 12 may be attached to PCB 10 bysoldering through coating 18 (without first removing coating 18) to formsolder joint 26 between electrical component 12 and conductive track 16of PCB 10. In other embodiments, electrical component 12 may be attachedto a coated PCB 10 by wire bonding electrical component 12 to conductivetrack 16 of PCB 10.

FIG. 9 illustrates a wire bond 84 that is formed through coating 18,according to certain embodiments. Wire bond 84 may be formed betweenwire 86 and any suitable surface. In some embodiments, wire bond 84 maybe formed between wire 86 and a surface of electrical component 12,conductive track 16, and/or circuit element. The surface on which wirebond 84 is formed may be referred to as a contact surface 88. In theillustrated embodiment, both wire 86 and contact surface 88 are coatedwith coating 18. In other embodiments, wire 86 may be coated and contactsurface 88 may be uncoated. In yet other embodiments, wire 86 may beuncoated and contact surface 88 may be coated. In some embodiments,coating 18 is only applied to the areas of wire 86 and/or contactsurface 88 where wire bond 84 is to be formed. In other embodiments,coating 18 is applied over all or substantially all of wire 86 and/orcontact surface 88.

The term “wire bonding” generally refers to a technique for joiningelectrical components 12 and/or circuit elements in the absence ofsolder 38 and/or flux 42. In some embodiments, wire bonding may be usedto make an electrical connection between two or more components using aconductive wire 86. Wire bonding may be used to make interconnectionsbetween an integrated circuit in bare die form and the leadframe insidethe integrated circuit. In addition, or alternatively, wire bonding maybe used to make interconnections between a bare die and PCB 10.

Wire bond 84 may be formed on contact surface 88 using wire 86 and awire bonder 90. Wire bond 84 may be formed using any suitable type ofwire 86. The term “wire” may refer to one or more elongated strands ofconductive material. In some embodiments, wire 86 may carry anelectrical current, transmit an electrical signal, and/or bear amechanical load. In some embodiments, wire comprises a pin, a filament,an electrical lead, and/or a leg of electrical component 12.

Wire 86 may comprise any suitable material. In some embodiments, wire 86comprises one or more conductive materials such as, for example, commonmetals, precious/rare metals, conductive polymers, and/or conductivenon-metallic materials. In a preferred embodiment, wire 86 comprisesgold, aluminum, copper, and/or silver. In other embodiments, wire 86comprises nickel, palladium, platinum, rhodium, iridium, tin, lead,germanium, antimony, bismuth, indium, gallium, cobalt, iron, manganese,chromium, vanadium, titanium, scandium, zirconium, molybdenum, tungsten,other transitional metals, and/or other suitable materials. Wire 86 maycomprise any suitable metal alloy and/or combination of conductivematerials. In some embodiments, wires 86 comprising metals (includingalloys) that readily oxidize and/or tarnish may especially benefit fromcoating 18. Applying coating 18 to wires 86 may extend the shelf lifeand/or functional life of devices comprising wires 86.

Wire 86 may have a cross section that is circular, rectangular, or anyother suitable shape. In some embodiments, wire 86 having a rectangularcross section is referred to as a ribbon. In embodiments where wire 86has a circular cross section, wire 86 may have diameter 92 in the rangeof five μm to one mm. In other embodiments, wire 86 has diameter 92 inthe range of ten μm to two hundred μm. In a preferred embodiment, wire86 has diameter 92 in the range of fifteen μm to seventy-five μm. Inembodiments where wire 86 has a rectangular cross section, a side ofwire 86 may have a dimension in the range of five μm to one mm. In otherembodiments, a side of a rectangular wire 86 may have a dimension in therange of ten μm to two hundred μm. In a preferred embodiment, a side ofa rectangular wire 86 may have a dimension in the range of twenty μm toseventy-five μm. Different types of wires 86 may require different wirebonding equipment and/or parameters.

Wire bonder 90 is generally operable to form wire bond 84 between wire86 and contact surface 88. Wire bonder 90 may be any suitable type ofmachine that uses heat and/or pressure to form bonds between wires 86and contact surfaces 88. Wire bonder 90 may be a wedge-wedge wire bonder90, a ball-wedge wire bonder 90, a three way convertible wire bonder 90,an ultrasonic insulated wire bonder 90, a high frequency wire bonder 90,a manual wire bonder 90, and automatic wire bonder 90, and/or anysuitable type of wire bonder 90. In some embodiments, wire bonder 90comprises a needle-like tool (referred to as a capillary) through whichwire 86 is threaded. Wire bonder 90 may position an end of wire 86 oncontact surface 88 to form either a ball bond 84 a or a wedge bond 84 b.The terms “ball” and “wedge” generally refer to the geometry of wire 86at the point where the connection is made. These two methods of wirebonding—ball bonding and wedge bonding—may use different combinations ofheat, pressure, and/or ultrasonic energy to make a weld at either orboth ends of wire 86.

In some embodiments, wire bonder 90 forms ball bond 84 a by applying ahigh-voltage electric charge to wire 86, which may melt wire 86 at thetip of the capillary of wire bonder 90. The tip of wire 86 may form intoa ball due to the surface tension of the molten metal. Before, during,or after the ball solidifies, wire bonder 90 may actuate the capillary,causing the end of wire 86 to touch contact surface 88. Wire bonder 90may then apply heat, pressure, and/or ultrasonic energy to create a weldbetween the end of wire 86 and contact surface 88. Thus, wire bonder 90may form ball bond 84 a. FIG. 10A illustrates a microscope image of ballbonds 84 a formed between uncoated wires 86 and a coated contact surface88, according to certain embodiments. Wires 86 and contact surface 88may comprise any suitable type and/or combination of conductivematerials. In the illustrated embodiment, wire 86 comprises gold andcontact surface 88 comprises copper. Contact surface 88 may bepre-treated before coating 18 is applied to contact surface 88. In theillustrated example, contact surface 88 was pre-treated with a liquidbased sulphuric acid/hydrogen peroxide solution. After drying, theexample contact surface 88 was then treated with hydrogen plasma, afterwhich coating 18 was deposited on contact surface 88. In the illustratedexample, ball bond 84 a between wire 86 and contact surface 88 wereformed after coating 18 was deposited on contact surface 88. Althoughthe foregoing example illustrates contact surface 88 that waspre-treated with a particular solution and hydrogen plasma, it should beunderstood that any suitable surface treatment may be used prior toapplying coating 18. It should be further understood that, in someembodiments, no surface treatment of contact surface 88 may occur priorto applying coating 18.

FIG. 10B illustrates a microscope image of a section view of ball bond84 a between an uncoated wire 86 and a coated contact surface 88,according to certain embodiments. Wires 86 and contact surface 88 maycomprise any suitable type and/or combination of conductive materials.In the illustrated embodiment, wire 86 comprises gold and contactsurface 88 comprises copper. Contact surface 88 may be pre-treatedbefore coating 18 is applied to contact surface 88. In the illustratedexample, contact surface 88 was pre-treated with a liquid basedsulphuric acid/hydrogen peroxide solution. After contact surface 88dried, coating 18 was deposited on the example contact surface 88. Thecoated contact surface 88 in this example was then post treated with ahydrogen plasma. In this example, ball bond 84 a was then formed betweenwire 86 and contact surface 88.

Although the foregoing example illustrates contact surface 88 that waspretreated with a particular solution and post-treated with hydrogenplasma, it should be understood that contact surface 88 may receive anysuitable pre-treatment and/or post-treatment. It should be furtherunderstood that, in some embodiments, no surface treatment of contactsurface 88 may occur before or after applying coating 18.

In some embodiments, wire bonder 90 forms wedge bond 84 b between wire86 and contact surface 88. Wire bonder 90 may form wedge bond 84 b bycrushing wire 86 against contact surface 88. After forming wedge bond 84b, wire bonder 90 may cut wire 86. FIG. 11A illustrates a microscopeimage of wedge bonds 84 b between uncoated wires 86 and a coated contactsurface 88, according to certain embodiments. FIG. 11B illustrates amicroscope image of a section view of wedge bond 84 b between a coatedwire 86 and a coated contact surface 88.

Wire bonder 90 may be configured to form ball bond 84 a at one end ofwire 86 and to form wedge bond 84 b at the other end of wire 86. Thisprocess may be referred to as ball-wedge bonding. FIG. 12 illustratesPCB 10 having ball bond 84 a and wedge bond 84 b, according to certainembodiments. In some embodiments, wire bonder 90 may first form ballbond 84 a between contact surface 88 and a molten, spherical ball at theend of wire 86. Ball bond 84 a may be formed using thermal and/orultrasonic energy. Wire bonder 90 may then use wire 86 to form a loop ofa desired height and shape. Once the loop is in the desired position forformation of a second bond, wire bonder 90 may form wedge bond 84 bbetween wire 86 and contact surface 88. After forming wedge bond 84 b,wire bonder 90 may cut wire 86, leaving a free end that can be formedinto a spherical ball which can be used to form the next wire bond 84.

In some embodiments, wire bonder 90 may be configured to form wedgebonds 84 b at both ends of wire 86. This process may be referred to aswedge-wedge bonding. Wedge bonding may rely on a combination ofultrasonic and frictional energy. Wedge bond 84 b may be formed with orwithout a contribution of additional thermal energy introduced byheating wire 86. In some embodiments, wedge bonds 84 b may be preferredfor connecting wires 86 to conductive tracks 16 of PCB 10.

Generally, a good wire bond 84 may be achieved by using wire 86 andcontact surface 88 that are free or substantially free of contaminantssuch as, for example, oxidation products. Traditionally, achieving goodwire bonds 84 using copper wire 86 has been difficult because copperreadily oxidizes under normal atmospheric conditions. Layers of copperoxide on the surface of wire 86 and/or contact surface 88 may make theformation of wire bonds 84 difficult. In addition, the elevatedtemperatures required for wire bonding may lead to increased oxidation.As a result, manufacturers either have avoided using wire 86 thatreadily oxidizes (e.g., copper wire) or have required the use of inertatmospheres to prevent oxidation. In some cases, manufacturers try toclean copper wires 86 immediately before wire bonding to remove build-upof copper oxide and/or other tarnishes from the surface of the copperwires 86. Cleaning of the copper wires 86 and/or using inert atmosphereshave introduced complications and expense to the wire bonding process.As a result, some types of wire 86 (e.g., copper wire) have not beencommonly used in wire bonding.

Applying coating 18 to wire 86 and/or contact surface 88 may alleviatesome, all, or none of the above problems. In some embodiments, applyingcoating 18 comprising a halo-hydrocarbon polymer to wire 86 and/orcontact surface 88 may protect wire 86 and/or contact surface 88 fromoxidation and/or corrosion. Thus, coating 18 may prevent the formationof oxide and/or corrosive layers that would hinder the bonding of wire86 to contact surface 88. In some embodiments, coating 18 may beconfigured such that wire bonds 84 can be formed through coating 18without the prior removal of coating 18 from wire 86 and/or contactsurface 88. By preventing oxidation and/or by allowing wire bonds 84 tobe formed through coating 18, coating 18 may reduce the expense and/ordifficulty of the wire bonding process.

In some embodiments, both wire 86 and contact surface 88 are coated withcoating 18. Coating 18 on wire 86 may be identical or substantiallyidentical to coating 18 on contact surface 88. Alternatively, coating 18on wire 86 may comprise different halo-hydrocarbon polymers than coating18 on contact surface 88. In other embodiments, wire 86 is uncoated andcontact surface 88 is coated with coating 18. In yet other embodiments,wire 86 is coated with coating 18 and contact surface 88 is uncoated.Coating 18 on wire 86 and/or contact surface 88 may be continuous,substantially continuous, or non-continuous. A continuous orsubstantially continuous coating 18 may be preferred for high levels ofprotection from harmful environments. Non-continuous coatings 18 may bepreferred for other purposes.

Coating 18 on wire 86 and/or contact surface 88 may have any suitablethickness 24. In some embodiments, thickness 24 of coating 18 is fromone nm to two μm. In other embodiments, thickness 24 of coating 18 isfrom one nm to five hundred nm. In yet other embodiments, thickness 24of coating 18 is from three nm to five hundred nm. In yet otherembodiments, thickness 24 of coating 18 is from ten nm to five hundrednm. In yet other embodiments, thickness 24 of coating 18 is from ten nmto two hundred and fifty nm. In yet other embodiments, thickness 24 ofcoating 18 is from ten nm to thirty nm. In yet other embodiments,coating 18 is a monolayer of a halo-hydrocarbon polymer (e.g., havingthickness 24 of a few angstroms (Å)). In a preferred embodiment,thickness 24 of coating 18 is from ten nm to one hundred nm in variousgradients, with one hundred nm being a preferred thickness 24. Coating18 on wire 86 and/or contact surface 88 may be a single-layer coating 18or a multi-layer coating 18.

The optimal thickness 24 of coating 18 may depend on the particularproperties that are desired for wire 86 and/or contact surface 88 afterwire bond 84 is formed. For example, if one desires a high level ofcorrosion resistance, abrasion resistance, and/or environmentaltoughness, a thicker coating 18 may be desired. Thus, thickness 24 ofcoating 18 may be configured and/or optimized for the particularrequirements of a device.

As explained above, coating 18 may be configured so that wire bonder 90can form wire bond 84 through coating 18. In other words, wire bonder 90may be operable to bond wire 86 to contact surface 88 without firstremoving coating 18 from wire 86 and/or contact surface 88. Thus, thewire bonding process may selectively alter coating 18 in the area ofwire bond 84. In some embodiments, coating 18 is selectively removedfrom wire 86 and/or contact surface 88 by the wire bonding process onlyin the local area of wire bond 84 such that coating 18 remains intactright up to wire bond 84. Thus, coating 18 may abut wire bond 84 afterwire bond 84 is formed. In some embodiments, coating 18 remains intacton wire 86 and/or contact surface 88 everywhere except where wire bond84 is made. Because coating 18 may remain intact right up to wire bond84, coating 18 may protect wire 86, contact surface 88, and/or theremainder of the device from oxidation, corrosion, and/or environmenteffects after wire bond 84 is formed. Thus, coating 18 may providelong-term stability and protection for a device.

In some embodiments, coating 18 on wire 86 and/or contact surface 88 isdisplaced by the action and/or processes of wedge bonding and/or ballbonding. In these bonding methods, energy may be effectively coupledinto the region of wire bond 84. This energy may facilitate thedisplacement of coating 18 on contact surface 88 and/or wire 86 andenable the formation of wire bond 84. As explained above, wedge bondingmay rely on a combination of ultrasonic and frictional energy with orwithout a contribution of additional thermal energy introduced byheating wire 86. In contrast, ball bonding may be primarily athermosonic process. For both wedge bonding and ball bonding, coating 18may be displaced selectively in the region of wire bond 84 by frictionaland/or thermal action. As a result, coating 18 may be displaced aseither a solid material, by a phase change, and/or by vaporisation.

Wire bonds 84 that are formed through coating 18 between wires 86 and/orcontact surfaces 88 may exhibit good bond strength. In some embodiments,wire bond 84 is strong enough that any failure will occur in wire 86prior to occurring in the interface between wire bond 84 and contactsurface 88. Thus, the bond strength may be greater than, less than, orequal to the failure strength of wire 86. In embodiments where wire 86has diameter 92 of twenty-five μm, five g to twelve g of force may berequired to break wire bond 84. In embodiments where wire 86 hasdiameter 92 of twenty-five μm, seven g to twelve g of force may berequired to break wire bond 84. The strength of wire bond 84 may beenhanced by cleaning wire 86 and/or contact surface 88 prior to applyingcoating 18. In some embodiments, wire 86 and/or contact surface 88 maybe treated by gas plasma to achieve a “super clean” surface. Activationand cleaning of wire 86 and/or contact surface 88 by gas plasma mayprovide stronger wire bonds 84.

In some embodiments, the strength of wire bond 84 may be measured usinga pull strength tester. The measurements may be repeated for differentthicknesses 24 of coating 18 on contact surface 88 and for differenttypes of wires 86. In one example, a Kullicke & Soffe 4523 wedge wirebonder 90 was used to form wire bonds 84. In this example, the wirebonder 90 was set to the following settings: (i) “First Bond” set to“Power 2.20,” “Time 4.0,” “Force 3.0=60 g”; (ii) “Second Bond” set to“Power 2.20”, “Time 3.0”, “Force 3.0=60 g”; (iii) electronics setting of“Long Time” interval. In this example, wire bonder 90 formed wire bonds84 between wires 86 listed in the table below and a copper contactsurface 88 that was coated with coating 18 comprising halo-hydrocarbonpolymers. Prior to applying coating 18, the copper contact surface 88was pre-treated with a liquid based sulphuric acid/hydrogen peroxidesolution.

After wire bonds 84 were formed in this example, a Kullicke & Soffe BT22pull strength tester was used to measure the strength of wire bonds 84.The measurements from this example are listed in the following table:

Wire material Nominal coating thickness Average bond strength (diameterμm) (nm) (g) Gold (25 μm) ~50 5.60 Gold (25 μm) ~80 8.46 Aluminium (25μm) ~30 7.65 Aluminium (25 μm) ~50 10.87 Aluminium (25 μm) ~80 7.00Copper (25 μm) ~60 8.60 Copper (25 μm) ~40 6.65In this example, the gold and aluminium wires 86 were uncoated and thecopper wires 86 were coated with coating 18 comprising halo-hydrocarbonpolymers. Prior to coating 18, the copper wires 86 were pre-treated forapproximately two minutes using hydrogen plasma. In each of the pullstrength tests in this example, it was observed that the point ofeventual failure was due to wire 86 breaking rather than wire bond 84failing. Thus, for this example, the bond strengths in the tableeffectively represent a lower limit of average bond strengths.

Although the foregoing example illustrates bond strengths for wire bonds84 between particular types of wires 86 and contact surfaces 88, itshould be understood that wire bond 84 may be formed between anysuitable type of wire 86 and any suitable type of contact surface 88.Although the foregoing example illustrates a particular type of wirebonder 90, it should be understood that any suitable type of wire bonder90 may be used to form wire bonds 84. Although the foregoing exampleillustrates particular thicknesses 24 of coating 18 on contact surface88, it should be understood that coating 18 on contact surface 88 and/orwire 86 may have any suitable thickness 24. In some embodiments,modifying the surface roughness of wire 86, contact surface 88, and/orcoating 18 may increase the strength of wire bond 84. Wire 86, contactsurface 88, and/or coating 18 may be configured with the same ordifferent surface roughnesses to optimize wire bonds 84 for variousapplications. In some embodiments, the surface roughness of wire 86and/or contact surface 88 may be modified prior to applying coating 18.In some embodiments, surface roughness of coating 18 may be modifiedafter it is applied to wire 86 and/or contact surface 88.

The surface roughness of wire 86, contact surface 88, and/or coating 18may be controlled on a macro scale (e.g., equal or greater than one μm)and/or on a micro scale (e.g., less than one μm). Modifying the surfaceroughness and/or flatness of wire 86 and/or contact surface 88 may ineffect modify contact area between and/or the frictional characteristicsof wire 86 and/or contact surface 88 during the wire bonding process.These types of modifications may allow energy to be efficiently coupledto the region of wire bond 84 during the wire bonding process. Thesemodifications may allow the formation of strong wire bonds 84 betweenwire 86 and contact surface 88.

The surface roughness, frictional characteristics, and/or surface energycharacteristics of wire 86, contact surface 88, and/or coating 18 may bemodified by any suitable method such as, for example, gas plasmatreatment, liquid/acid etching, mechanical treatment, and/or theselection of precursor compounds 36 for deposition of coating 18 (e.g.,chlorine).

In some embodiments, coating 18 is not removed from wire 86 and/orcontact surface 88 prior to the wire bonding process. In otherembodiments, coating 18 may be selectively removed from wire 86 and/orcontact surface 88 prior to the wire bonding process. In yet otherembodiments, prior to the wire bonding process, coating 18 may beremoved from wire 86 completely and/or from the whole area of contactsurface 88. In embodiments where at least a portion of coating 18 isremoved prior to the wire bonding process, coating 18 may be removedselectively or from a general area by heating contact surface 88, bylaser ablation, by plasma processing, and/or by liquid chemical etching.In such embodiments, coating 18 may be replaced after wire bond 84 isformed. In other embodiments, coating 18 may be applied after wirebonding, either onto a clean contact surface 88 or a pre-coated contactsurface 88. Such a step might be considered, for example, where longterm stability is required with the option of subsequent processing orrework at a later time. In some embodiments, once wire bond 84 isformed, wire 86, contact surface 88, and/or wire bond 84 are furtherprotected by applying an additional overlayer of coating 18.

Coating 18 may be applied to wire 86 and/or contact surface 88 using anysuitable technique. For example, coating 18 may be deposited usingchemical vapour deposition (CVD), molecular beam epitaxy (MBE), plasmaenhanced-chemical vapour deposition (PE-CVD), high pressure/atmosphericplasma deposition, metalloorganic-chemical vapour deposition (MO-CVD),and/or laser enhanced-chemical vapour deposition (LE-CVD). In someembodiments, coating 18 may be deposited by the creation ofinter-penetrating polymer networks (IPNs) and/or by surface absorptionof monolayers (SAMs) of polymers or monomers to form in-situ polymersand/or polymer alloys. In other embodiments, coating 18 may be depositedusing a liquid coating technique such as, for example, liquid dipping,spray coating, spin coating, sputtering, and/or a sol-gel process. Insome embodiments, wire 86 and/or contact surface 88 may be coated withcoating 18 shortly after manufacture in order to prevent oxidation.

In some embodiments, coating 18 may be deposited on wire 86 and/orcontact surface 88 by plasma deposition, as described above with respectto FIG. 2. In such embodiments, wire 86 and/or contact surface 88 may beplaced in chamber 30 and reactor 28 may introduce gases (e.g., hydrogen,argon, and/or nitrogen) into chamber 30 to clean wire 86 and/or contactsurface 88. Reactor 28 may then introduce one or more precursorcompounds 36 into chamber 30 to form a single-layer coating 18 ormulti-layer coating 18 on wire 86 and/or contact surface 88. In someembodiments, coating 18 may encapsulate and/or follow the threedimensional form of wire 86 and/or contact surface 88.

In some embodiments, coating 18 on wire 86 and/or contact surface 88 maycomprise a very thin layer (e.g., five nm or less) of a metal halide(preferably metal fluoride) directly in contact with the surface of wire86 and/or contact surface 88. The thin layer of metal halide maycomprise a minimal amount of halo-hydrocarbon material (e.g., less thanone percent by weight, less than five percent by weight, etc.). In someembodiments, the metal halide layer may be a monolayer, substantially amonolayer, or a few monolayers. In other embodiments, the metal halidelayer may comprise a metal halide zone of layers at the surface of wire86 and/or contact surface 88. The metal halide layer may be robust, maybe inert, and/or may prevent the formation on wire 86 and/or contactsurface 88 of oxide layers and/or tarnishes which may prevent effectivewire bonding.

In embodiments where coating 18 is applied by plasma deposition, themetal halide layer may form on wire 86 and/or contact surface 88 whenactive species in the gas plasma react with the metal surface. In someembodiments, the metal halide layer may be enhanced using a higherconcentration of fluorine species. A layer of coating 18 comprising ahalo-hydrocarbon polymer may then be deposited on and/or in combinationwith the metal halide layer. The layer of metal halide and the layer ofhalo-hydrocarbon polymers may be discrete, axially or spatially.Alternatively, there may be a graded transition from metal halide tohalo-hydrocarbon polymer in coating 18. In some embodiments, the metalhalide layer may protect wire 86 and/or contact surface 88 fromoxidation while the layer of halo-hydrocarbon polymers (i) may provideenvironmental protection from corrosive gases and/or liquids and/or (ii)may provide oxidation protection. Should the layer of halo-hydrocarbonpolymers in coating 18 eventually be worn away by mechanical abrasion,the underlying metal halide layer may prevent oxidation build-up, thusprotecting and prolonging the life of a device.

In some embodiments, coating 18 may permit wire 86 and/or contactsurface 88 to be wire bonded in a non-inert atmosphere withoutoxidizing. The term non-inert atmosphere refers to an atmospherecomprising gases (e.g., oxygen) that would normally oxidize and/orcorrode uncoated wires 86 and/or uncoated contact surfaces 88. Asexplained above, inert atmospheres were traditionally used to form wirebonds with uncoated copper wires 86. Inert atmospheres typicallycomprised inert gases such as, for example, nitrogen and/or argon.Because coating 18 may protect wire 86 and/or contact surface 88 fromoxidation and/or corrosion, coating 18 may permit wire bond 84 to beformed in a non-inert atmosphere with little or no risk of oxidation.Thus, coating 18 may reduce the cost and/or increase the efficiency ofthe wire bonding process. It should be understood, however, that coating18 may be used on wires 86 and/or contact surfaces 88 regardless ofwhether the wire bond 84 is formed in an inert or non-inert atmosphere.

Although the present invention has been described in severalembodiments, a myriad of changes and modifications may be suggested toone skilled in the art, and it is intended that the present inventionencompass such changes and modifications as fall within the scope of thepresent appended claims.

What is claimed is:
 1. A printed circuit board, comprising: a substratecomprising an insulating material; a plurality of conductive tracksattached to at least one surface of the substrate; a coating depositedon the at least one surface of the substrate, wherein: the coatingcovers at least a portion of the plurality of conductive tracks; andcomprises at least one halo-hydrocarbon polymer; and at least oneconductive wire that is connected by a wire bond to at least oneconductive track at a particular region of the substrate, the wire bondformed through the coating without prior removal of the coating suchthat the wire bond connects the at least one conductive wire directly tothe at least one conductive track at the particular region and thecoating abuts the wire bond at the particular region.
 2. The printedcircuit board of claim 1, wherein the wire bond abuts the coating alonga plane parallel to the at least one surface of the substrate.
 3. Theprinted circuit board of claim 1, wherein the wire bond is at least oneof: a ball bond; and a wedge bond.
 4. The printed circuit board of claim1, wherein the wire comprises at least one of: gold; aluminum; silver;copper; nickel; and iron.
 5. The printed circuit board of claim 1,wherein at least a portion of the wire is covered with the coating. 6.The printed circuit board of claim 1, wherein the coating has athickness of from 1 nanometers to 2 micrometers.
 7. The printed circuitboard of claim 1, wherein the coating has a thickness of from 10nanometers to 100 nanometers.
 8. The printed circuit board of claim 1,wherein the at least one halo-hydrocarbon polymer is afluoro-hydrocarbon polymer.
 9. The printed circuit board of claim 1,wherein the wire bond is formed at the particular region of thesubstrate, the formation of the wire bond altering the coating at theparticular region without altering the coating at other regions of thesubstrate.
 10. The printed circuit board of claim 9, wherein: thecoating is not removed from the particular region of the substrate priorto the formation of the wire bond; and the formation of the wire bondalters the coating at the particular region of the substrate byselectively removing the coating from the particular region of thesubstrate.
 11. The printed circuit board of claim 1, further comprisingat least one electrical component connected by a solder joint to atleast one conductive track, wherein the solder joint is soldered throughthe coating such that the solder joint abuts the coating.
 12. Theprinted circuit board of claim 1, wherein the wire bond is formed at afirst region of the substrate, the first region coated with the coating,and further comprising: at least one electrical component connected by asolder joint to at least one conductive track at a second region of thesubstrate, the second region coated with another coating.
 13. Theprinted circuit board of claim 1, further comprising a contact attachedto at least one surface of the substrate, the contact coated with thecoating, the contact operable to conduct an electrical signal throughthe coating to another contact.
 14. The printed circuit hoard of claim1, wherein the coating is deposited such that a metal halide layercovers at least a portion of the plurality of conductive tracks.
 15. Theprinted circuit board of claim 1, wherein the coating is deposited suchthat there is essentially no metal halide layer between the plurality ofconductive tracks and the coating.